                               In the

 United States Court of Appeals
               For the Seventh Circuit

No. 07-3929

U NITED STATES OF A MERICA,
                                                      Plaintiff-Appellee,

                                   v.

A BRAHAM COLON,
                                                 Defendant-Appellant.


             Appeal from the United States District Court
         for the Northern District of Illinois Eastern division.
             No. 06 CR 819—Virginia M. Kendall, Judge.



    A RGUED N OVEMBER 4, 2008—DECIDED D ECEMBER 8, 2008




  Before POSNER, W OOD, and TINDER, Circuit Judges.
  POSNER, Circuit Judge. The defendant was convicted by a
jury of possessing cocaine with intent to sell it, conspiring
to possess cocaine with intent to sell it, and aiding and
abetting the conspiracy, and he was sentenced to 135
months in prison. The principal ground of his appeal is that
he was not a conspirator or an aider and abettor of a
conspiracy, but was merely a purchaser from a conspirator,
2                                                   No. 07-3929

and that the jury’s contrary finding lacked sufficient basis in
the evidence to stand. He also challenges on Fourth Amend-
ment grounds his conviction of possession, and we start
there.
   The government was listening to the phone conversations
of the defendant’s supplier, Saucedo, and heard him tell
Rodriguez (Saucedo’s admitted co-conspirator) that “Dude”
would be coming to a particular house in 15 minutes to pick
up drugs that “Dude” had ordered. Sure enough, 15
minutes later, officers staking out the house saw a man
enter it and emerge shortly afterwards, and they tried to
stop him and after a chase caught him and found the
cocaine he had just bought. The man was Colon. The
cocaine was introduced into evidence against him at the
trial. He argues that merely knowing that a house is one in
which drugs are sold doesn’t create probable cause to stop
everyone who enters it. That is true in general, Ybarra v.
Illinois, 444 U.S. 85, 94-96 (1979); United States v. Johnson, 170
F.3d 708 (7th Cir. 1999); cf. United States v. Mitchell, 783 F.2d
971 (10th Cir. 1986), but the police had reason to believe that
the man who entered the house was indeed the expected
buyer. He arrived when Saucedo told Rodriguez the buyer
would arrive, and during the preceding 15 minutes no one
else had entered the house from the street (some persons
had entered from the porch of the house). So it was more
than suspicion or a guess that the man the police seized was
a buyer, and so the defendant’s challenge to his conviction
of possession fails.
  His challenge to his conviction of conspiracy and of aiding
and abetting a conspiracy has far more substance. The
No. 07-3929                                                 3

evidence of his guilt of these offenses, as summarized in the
government’s brief, is that the “defendant regularly ob-
tained distribution quantities of cocaine from Saucedo and
Rodriguez. . . . The dealings between . . . [the defendant and
Saucedo, with whom alone the defendant dealt] were
standardized and exhibited mutual trust. Saucedo and
Rodriguez had a stake in defendant’s distribution activities
as well as their ongoing arrangement, given that their
profits depended on the success of defendant’s distribution
efforts. . . . [The defendant and Saucedo] conducted regular,
standardized transactions through which defendant ob-
tained cocaine in quantities of either 4.5 or 9 ounces at
consistent prices, and distributed it to customers. Defendant
and Saucedo regularly arranged deliveries by telephone,”
with defendant being the caller, using Saucedo’s cellphone
number.
  The government’s summary describes a routine buyer-
seller relationship, as in United States v. Mercer, 165 F.3d
1331, 1336 (11th Cir. 1999), where the court remarked that
“the evidence shows simply that his co-defendant Miller
knew that Mercer sold drugs and that he had sources from
which he could get drugs, that Mercer had a source for
drugs and if that source failed he would ‘go somewhere
else,’ that he bought quantities of cocaine from some
unknown source and sold it to police agents presumably at
a profit.” The relationship in the present case was “stan-
dardized” only in the sense that because seller and buyer
dealt regularly with each other, the sales formed a regular
pattern, as one would expect in any repeat purchase,
legal or illegal. The length of the sales relationship is
unclear; it may have been as long as six weeks, but the
4                                                  No. 07-3929

total number of sales was no more than six or seven,
involving a total of 30 to 35 ounces of cocaine.
  In any event, how “regular” purchases on “standard”
terms can transform a customer into a co-conspirator
mystifies us. “[A]greement—the crime of conspir-
acy—cannot be equated with repeated transactions.” United
States v. Thomas, 150 F.3d 743, 745 (7th Cir. 1998). The
government either is confusing buying with conspiring or
believes that a seller and buyer who fail to wrangle over
each sale aren’t dealing at arms’ length and therefore lack
mutual trust. But “mutual trust” is already a factor in the
conventional analysis of conspiracy; an act that is merely
evidence of mutual trust cannot be a separate factor. And
anyway repeat transactions need not imply greater
mutual trust than is required in any buyer-seller relation-
ship. If you buy from Wal-Mart your transactions will be
highly regular and utterly standardized, but there will be
no mutual trust suggestive of a relationship other than
that of buyer and seller.
  It is different if, as in United States. v. Sax, 39 F.3d 1380,
1385-86 (7th Cir. 1994), a seller assists his customers in
establishing the methods by which they will take delivery
from him, for then he is more than just a seller; he is helping
to create a distribution system for his illegal product. But
the defendant in our case (a buyer, not a seller) did nothing
to help Saucedo and Rodriguez establish a delivery system
that would enable them to serve him, or serve him better.
  The fact that in his conversations with Rodriguez,
Saucedo referred to Colon as “Dude” or “Old Boy,” rather
than calling him by his name, is not, as the government
No. 07-3929                                                   5

believes, indicative of intimacy or a pre-existing relation-
ship; it is for obvious reasons a convention in the drug trade
not to refer to a customer by his real name. There were
no sales on credit to the defendant, or other evidence of
mutual trust or dependence, and he had no dealings
with—indeed, he never met or spoke to—Rodriguez,
Saucedo’s unquestioned co-conspirator, although the
defendant knew that they worked together. There is no
suggestion that the defendant could expect to receive any
part of the income that Saucedo obtained from selling
cocaine to other customers. There was no “stimulation,
instigation,” or “encouragement” by the defendant of
Saucedo and Rodriguez’s business, Direct Sales Co. v. United
States, 319 U.S. 703, 713 (1943), no “informed and interested
cooperation” between that business and the defendant’s
retail drug business. Id. In his conversations with Rodri-
guez, Saucedo referred to the defendant only as a “cus-
tomer,” not as an associate, colleague, pal, or “one of us.”
The prosecutor in closing argument described the defendant
as the conspirators’ customer, and its own witnesses denied
that Saucedo had ever asked the defendant to sell cocaine
for him or Rodriguez.
   Of course Saucedo and Rodriguez had, as the government
says, “a stake in defendant’s distribution activities.” Every
seller to a distributor has a stake in the distributor’s activi-
ties; a person who buys for resale will not enrich his seller
if his resale business dries up. Saucedo and Rodriguez had
other customers; we do not know how many, or what the
defendant’s volume of purchases was relative to that of
other customers.
6                                                 No. 07-3929

  Cases in this and other circuits list factors such as we have
discussed, along with others, as indicative of participation
in a conspiracy. But in every case such factors have to be
placed in context before an inference of participation in a
conspiracy can be drawn. See United States v. Moran, 984
F.2d 1299, 1302-03 (1st Cir. 1993). In United States v. Hicks,
368 F.3d 801, 805 (7th Cir. 2004), for example, we listed a
number of these factors but added “prolonged cooperation”
between the parties (a quotation from Direct Sales Co. v.
United States, supra, 319 U.S. at 713, the Supreme Court’s
leading case on the difference between a conspiracy and a
mere buyer-seller relationship) and “sales on credit,” factors
that strengthen an inference of participation drawn from
observing circumstances also found in a routine buyer-seller
relationship. See also United States v. Hawkins, 2008 WL
4589396, at *7 (2d Cir. Oct. 16, 2008).
  So the government’s theory of conspiracy, when stripped
of its redundancies and irrelevancies, reduces to an asser-
tion that a wholesale customer of a conspiracy is a co-
conspirator per se. The implication is that during Prohibi-
tion a speakeasy was a co-conspirator of the smuggler who
provided it with its supply of booze. And the logic of the
government’s position does not stop with the customer
who is a wholesale purchaser rather than a retail one. Had
the defendant been purchasing for his personal consump-
tion, he would still have had “regular, standardized”
transactions with Saucedo, as in our Wal-Mart example, and
Saucedo would have had a stake in whatever activity the
defendant engaged in to obtain the money to buy cocaine.
There would have been the same level of “mutual trust” as
required in any illegal sale because either buyer or seller
No. 07-3929                                                  7

might be a government informant or turn violent. The
mutual trust in this case was less than it would have been
had Saucedo “fronted” cocaine to the defendant (a factor
mentioned in almost all the cases) rather than being paid in
cash at the time of sale. With fronting, the seller becomes the
buyer’s creditor, adding a dimension to the relationship that
goes beyond a spot sale for cash.
   There are practical reasons for not conflating sale with
conspiracy. “A sale, by definition, requires two parties; their
combination for that limited purpose does not increase the
likelihood that the sale will take place, so conspiracy
liability would be inappropriate.” United States v. Townsend,
924 F.2d 1385, 1394 (7th Cir. 1991) (citation omitted). As
we put it in United States v. Manzella, 791 F.2d 1263, 1265
(7th Cir. 1986), “A conspiracy involves more people and
can therefore commit more crimes; and it can do so more
efficiently, by exploiting the division of labor and by
arranging concealment more effectively—sometimes
through suborning law enforcers.” There is nothing like
that here, so far as the defendant’s involvement was con-
cerned. And the situation is not altered just because he was
a buyer for resale rather than for his personal consumption.
As the plurality opinion in United States v. Lechuga, 994 F.2d
346 (7th Cir. 1993) (en banc), explains, “before today, it was
widely assumed that a conviction for participation in a drug
conspiracy could be affirmed with no more evidence than
that the defendant had sold in a quantity too large to be
intended for his buyer’s personal consumption, though
some of our cases . . . tugged the other way. Today we
resolve the conflict in our cases by holding that ‘large
quantities of controlled substances, without more, cannot
8                                                   No. 07-3929

sustain a conspiracy conviction.’ What is necessary and
sufficient is proof of an agreement to commit a crime other
than the crime that consists of the sale itself.” Id. at 347
(citations omitted). (This part of the Lechuga opinion
reflected the view of the majority of the judges, as noted in
United States v. Dekle, 165 F.3d 826, 829 n. 3 (11th Cir. 1999).)
See also United States v. Thomas, 284 F.3d 746, 750 (7th Cir.
2002); United States v. Rivera, 273 F.3d 751, 755 (7th Cir.
2001); United States v. Wexler, 522 F.3d 194, 207-08 (2d Cir.
2008).
  The Eleventh Circuit pointed out in United States v. Dekle,
supra, 165 F.3d at 829, that “what distinguishes a conspiracy
from its substantive predicate offense is not just the pres-
ence of any agreement, but an agreement with the same
joint criminal objective—here the joint objective of distribut-
ing drugs. This joint objective is missing where the conspir-
acy is based simply on an agreement between a buyer and
a seller for the sale of drugs. Although the parties to the
sales agreement may both agree to commit a crime, they do
not have the joint criminal objective of distributing drugs.”
This would be a different case, therefore, had the defendant
agreed to look for other customers for Saucedo and Rodri-
guez, had received a commission on sales to those custom-
ers, had advised Saucedo and Rodriguez on the conduct of
their business, or had agreed to warn them of threats to
their business from competing dealers or from law-enforce-
ment authorities. It would be a different case if “Lechuga
[the seller] had told Pinto [the buyer] that he needed a good
distributor on the south side of Chicago and wanted to enter
into a long-term relationship with Pinto to that end. Then it
would be as if Lechuga had hired Pinto to assist him in
No. 07-3929                                                    9

reaching his market.” United States v. Lechuga, supra, 994
F.2d at 349.
  All these would be settings in which, in the Eleventh
Circuit’s terminology, Saucedo, Rodriguez, and the defen-
dant would have had “the same joint criminal objective . . .
of distributing drugs.” 165 F.3d at 829; see, e.g., United States
v. James, 540 F.3d 702, 707 (7th Cir. 2008); United States v.
Jarrett, 133 F.3d 519, 533-34 (7th Cir. 1998); United States v.
Romero, 57 F.3d 565, 569-70 (7th Cir. 1995); United States v.
Garcia, 45 F.3d 196, 198-99 (7th Cir. 1995); United States v.
Brown, 217 F.3d 247, 254-55 (5th Cir. 2000), vacated on
unrelated grounds under the name Rendle v. United States,
531 U.S. 1136 (2001); United States v. McCoy, 86 F.3d 139,
140-41 (8th Cir. 1996); United States v. Reynolds, 828 F.2d 46,
47 (1st Cir. 1987); United States v. Pozos, 697 F.2d 1238, 1241
(5th Cir. 1983). But in our case there is no evidence of a
relationship other than a conventional sales relationship
between the defendant and the conspiracy from which he
bought drugs. It is true that after discarding, in his flight
from the police, the cocaine he had just bought from
Saucedo, the defendant called Saucedo and told him what
had happened. But there is no suggestion that he was
warning Saucedo, in order to help the latter evade capture,
rather than merely reporting an incident that might affect
the defendant’s future purchases. A drug runner employed
by Saucedo phoned the defendant and told him he’d been
stopped by the police after delivering cocaine to him, but
that is not evidence of the defendant’s participation in a
conspiracy either.
 The muddle that was the government’s theory of the case
was mirrored in the jury instructions, which after correctly
10                                                No. 07-3929

noting that the defendant’s purchase of drugs from another
person for resale was insufficient evidence that the defen-
dant had conspired with that person, told the jury to
consider whether “the parties had an understanding that
the cocaine would be sold” and whether “the transaction
involved large quantities of cocaine.” If the defendant was
a middleman, as he was, the parties would understand that
he would be reselling the cocaine; and as a middleman he
would be likely to buy in quantities greater than one would
buy for one’s personal consumption, and therefore “large.”
The jury was also asked to consider whether the parties had
“a standardized way of doing business over time,” whether
they had “a continuing relationship,” “whether the sales
were on credit or on consignment,” and whether the seller
had a “financial steak [sic] in a resale by the buyer.” Only
the question about credit or consignment was germane, for
reasons that we’ve indicated, and that question could only
have confused the jury, since all the transactions with the
defendant were cash transactions. And the judge made no
effort to relate the factors that she told the jury to consider
to the difference between a customer and a conspirator. It is
no surprise that the jury convicted; given the warped
instructions, the conviction does nothing to advance the
government’s argument that the evidence of conspiracy was
sufficient for a reasonable jury to convict.
   Nor was the defendant proved to be an aider or abettor of
the Saucedo-Rodriguez conspiracy. An aider and abettor is
conventionally defined as one who knowingly assists an
illegal activity, wanting it to succeed. E.g., United States v.
Pino-Perez, 870 F.2d 1230, 1235 (7th Cir. 1989) (en banc);
United States v. Freeman, 434 F.3d 369, 377 (5th Cir. 2005);
United States v. Peoni, 100 F.2d 401, 402 (2d Cir. 1938) (L.
No. 07-3929                                                11

Hand, J.). This is a general definition, however, and like
most legal generalizations requires qualification in particu-
lar cases. Suppose you own and operate a store that sells
women’s clothing. Every month the same young woman
buys a red dress from your store. You happen to know that
she’s a prostitute and wears the dress to signal her occupa-
tion to prospective customers. By selling her the dress at
your normal price you assist her illegal activity, and
probably you want the activity to succeed since if it fails
she’ll stop buying the dress and your income will be less.
But you are not an aider and abettor of prostitution because
if you refused to sell to her she would buy her red dress
from another clothing store, one whose proprietor and staff
didn’t know her profession. United States v. Zafiro, 945 F.2d
881, 887 (7th Cir. 1991), affirmed on other grounds, 506 U.S.
534 (1993); see also United States v. Falcone, 109 F.2d 579,
581 (2d Cir. 1940) (L. Hand, J.). So you’re not really helping
her or promoting prostitution, as you would be if you
recommended customers to her in exchange for a commis-
sion.
  It is the same here, so far as the record reveals. By buying
from Saucedo, the defendant was assisting an illegal
activity, which he doubtless wanted to be successful as
otherwise he would have to find another seller. If that is
enough to establish aiding and abetting, every buyer from
a drug conspiracy is an aider and abettor of a conspiracy
and is therefore to be treated by the law exactly as a mem-
ber of the conspiracy would be treated. 18 U.S.C. § 2(a). Yet
as with the sale of the red dress, there is no basis for
thinking that the defendant really helped Saucedo and
Rodriguez’s drug conspiracy—that he made a differ-
12                                                 No. 07-3929

ence—because so far as appears they could have found
another customer for the modest amount of cocaine that
they sold to him.
  The government relies on United States v. Kasvin, 757 F.2d
887 (7th Cir. 1985), but omits mention of the part of the
opinion that shows how different that case is from this one.
Kasvin, the buyer defendant, “for several years . . . had
visited the headquarters of the conspiracy several times
weekly, had been assigned a number just as some of the
admitted members of the conspiracy had been assigned, his
telephone number had been encoded, on occasion he
provided the organization with marijuana for use in its
business, his transactions with the conspiracy ran into
hundreds of thousands of dollars annually but unlike an
ordinary customer of a business, he simply picked up
quantities of marijuana from headquarters, presumably
disposed of it through a distribution network, and brought
the money back from time to time in amounts which, so far
as the records show, bore no definite relationship to the
amounts of marijuana carried away at any particular time.”
Id. at 891. There is nothing like that here.
  We are mindful of cases such as United States v. Abuelhawa,
523 F.3d 415, 419-21 (4th Cir.), cert. granted, 2008 WL
3849383 (U.S. Nov. 14, 2008), and our own United States v.
Binkley, 903 F.2d 1130, 1135-36 (7th Cir. 1990), which hold
(contrary to the decisions of some other circuits, however)
that 21 U.S.C. § 843(b), which makes it unlawful “for any
person knowingly or intentionally to use any communica-
tion facility in . . . facilitating the commission of any act or
acts constituting a felony” in violation of the Controlled
No. 07-3929                                                  13

Substances Act, 21 U.S.C. §§ 801 et seq., is violated when a
person uses the phone to order drugs for his personal use.
But these decisions are based on the specific language of
section 843(b) rather than on the concept of aiding and
abetting.
  Even the government has its doubts whether the defen-
dant was a member or an aider and abettor of the Saucedo-
Rodriguez conspiracy. A conspirator is liable for the
foreseeable crimes that his co-conspirators commit in
furtherance of the conspiracy, Pinkerton v. United States, 328
U.S. 640, 646-47 (1946); United States v. Hach, 162 F.3d 937,
951 (7th Cir. 1998), yet the only drug quantity on which the
government sought to base the defendant’s sentence was
the quantity that Saucedo sold him, though he knew that
Saucedo and Rodriguez were selling cocaine to others as
well as to him. One is led to wonder why the government
added charges of conspiracy and of aiding and abetting to
the charge of possession with intent to distribute. The
guideline ranges were the same and the additional charges
were likely to confuse the jury by making the defendant’s
conduct seem more ominous than it was. Those charges
were not necessary to enable the government to introduce
an alleged co-conspirator’s (Saucedo’s) evidence against the
defendant, since when the question is the admissibility of
such evidence the judge decides, in ruling on its admissibil-
ity, whether there was a conspiracy. United States v. Yoon,
128 F.3d 515, 525-26 (7th Cir. 1997); United States v. Santiago,
582 F.2d 1128, 1130-31 (7th Cir. 1978), overruled on other
grounds by Bourjaily v. United States, 483 U.S. 171 (1981).
There needn’t be a charge of conspiracy.
14                                                No. 07-3929

  So probably the additional charges added nothing to the
charge of possession with intent to distribute. But maybe the
government was concerned that in the (unlikely) event that
the evidence obtained when the defendant was caught at
Saucedo’s house was suppressed, the jury might acquit the
defendant of possession or the sentence for possession
might be based on a smaller quantity of cocaine and
therefore be shorter.
  Since the defendant was given concurrent sentences on
the two counts, it may seem that reversing the conspiracy
and aiding and abetting count could not alter his sentence.
But the district judge sentenced him very near the top of the
applicable guideline range, and in doing so may have been
influenced by the fact that the jury had found the defendant
guilty of conspiracy and aiding and abetting as well as of
possession. Yates v. United States, 355 U.S. 66, 75-76 (1957);
United States v. Manzella, supra, 791 F.2d at 1270; United
States v. Triumph Capital Group, Inc., 544 F.3d 149, 171-72 (2d
Cir. 2008). So while the defendant’s conviction of possession
stands, he is entitled to be acquitted on the other count and
he must therefore be resentenced.

                       A FFIRMED IN PART, V ACATED IN PART,
                          AND REMANDED WITH D IRECTIONS.




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