Lamont Smith was convicted of one count of possession with the intent to distribute more than 50 grams of cocaine base in violation of 21 U.S.C. § 841. He was sentenced by the district court1 to 120 months’ imprisonment. On appeal, Smith argues (1) that the district court erred in denying his motion to suppress and (2) that the district court erred in permitting a previously undisclosed witness to testify on rebuttal. We affirm.
I.
A.
On April 13, 2001, Hawthorne, California, police officer Melanie Newenham, who was participating in a “parcel interdiction” operation at a Federal Express (“FedEx”) facility in Hawthorne, removed a suspicious looking package from a conveyor belt. After removing .the package, she gave it to Detective Julian Catano, who, also believing the package to be suspicious, decided to submit it to a canine sniff. The dog alerted to the package, signifying that it contained illegal drugs. Detective Cata-no took the package to Lee Edwards, the FedEx facility manager, and told her that he suspected that the package contained drugs. Edwards asked whether Catano wanted her to open the package. Detective Catano testified that he told her that “if she wanted to open it that would be fine .... ” Edwards opened the box, revealing a pair of children’s rubber boots. Inside one of the boots, she found a ball of clear tape containing a white substance. Detective Catano and Officer Newenham took the package to the Hawthorne police station, where it and its contents were examined and photographed. The package was later resealed and returned to the FedEx facility for controlled shipment to the recipient address in Lincoln, Nebraska. Controlled delivery was executed at the recipient address, where the package was accepted by Smith, who identified himself by the alias “Sergio.”
Smith moved to suppress the cocaine base found in the package. The district court denied the motion, adopting the recommendation of the magistrate *704judge.2 We review de novo the district court’s interpretation of the protections afforded by the Fourth Amendment, and we review for clear error its factual determinations. United States v. Lothridge, 332 F.3d 502, 503-04 (8th Cir.2003).
B.
Smith contends that Officer Newenham unlawfully seized the package. A law enforcement officer must have reasonable suspicion that a piece of mail, or a package shipped via a commercial carrier, contains contraband to lawfully seize it for investigative purposes. United States v. Johnson, 171 F.3d 601, 603 (8th Cir.1999). Seizure occurs when a package is removed from its ordinary progress in the mail and is diverted for further investigation. Id. An officer has reasonable suspicion that a package contains contraband if she has “a particularized and objective basis” that is more than an “inchoate and unparticularized suspicion or hunch.” Id. (quoting Terry v. Ohio, 392 U.S. 1, 27, 88 S.Ct. 1868, 20 L.Ed.2d 889 (1968)). The officer must be able to explain the basis of her suspicion. Id. at 604. The officer may cite as the basis of her belief, however, facts which, alone and to an untrained eye, appear innocuous, but which, to a trained officer familiar with the methods of drug traffickers, are sufficient to establish reasonable suspicion. Id.; United States v. Demoss, 279 F.3d 632, 636 (8th Cir.2002).
We turn to the question whether Officer Newenham had reasonable suspicion that the package contained contraband when she seized it. We conclude that she did. She was able to articulate a number of factors that led to her conclusion: the package was sent from California; it was a Sony cordless telephone box; its air bill was handwritten; it was shipped via overnight delivery; and it was marked for optional Saturday delivery. After lifting the package from the conveyor belt, which was not in and of itself a seizure, Demoss, 279 F.3d at 635, Newenham observed that the sender’s address had been scratched out and rewritten and that the cost of shipping had been paid in cash. Taken individually, each of the foregoing facts is consistent with innocent conduct. Indeed, taken collectively, the coexistence of these characteristics might well be seen as innocent by the average citizen. New-enham’s training and experience, however, gave her a reasonable basis for her determination that the package was suspicious. She knew that the package was shipped from a drug source state. She knew that the type of telephone is commonly available throughout the United States, and she was therefore suspicious as to why someone would choose to ship one via FedEx, especially given the high cost of overnight and Saturday delivery — approximately $35 for shipping versus approximately $60 for the phone. She knew that drug traffickers commonly use overnight and Saturday delivery to minimize the amount of time illicit materials are subject to investigation by the shipping company. She knew that drug traffickers commonly wait until the last possible moment to address packages containing drugs by hand to reduce the likelihood that the recipient’s address will be discovered if the shipper is stopped by a law enforcement officer. She thought it suspicious that a sender would make an error in writing his or her own address. And she knew from her training and experience that drug traffickers often pay for shipping in cash. These facts provided Newenham with a “particularized and ob*705jective basis” for seizing the package, and thus she did not act on the basis of some “inchoate and unparticularized suspicion or hunch.” Terry, 392 U.S. at 27, 88 S.Ct. 1868; United States v. Logan, 362 F.3d 530, 533-34 (8th Cir.2004) (noting that drug source state, overnight shipping, and handwritten air bill contribute to finding of reasonable suspicion that a package contained contraband). Thus, her seizure of the package was lawful.
C.
We next consider Smith’s argument that Lee Edwards acted as an agent of the government in opening the box, thereby tainting discovery of the cocaine base. A search by a private citizen is not subject to the strictures of the Fourth Amendment unless that private citizen is acting as a government agent. United States v. Malbrough, 922 F.2d 458, 461-62 (8th Cir.1990). We look to several factors in determining whether a private citizen was acting as an agent of the government. Chief among these are whether the government had knowledge of and acquiesced in the intrusive conduct; whether the citizen intended to assist law enforcement agents or instead acted to further his own purposes; and whether the citizen acted at the government’s request. Id. at 462 (citing United States v. Miller 688 F.2d 652, 656-57 (9th Cir.1982)); United States v. Hollis, 245 F.3d 671, 674 (8th Cir.2001); United States v. Parker, 32 F.3d 395 (8th Cir.1994). Because the government certainly knew of, and acquiesced in, the opening of the package, this is a much closer case than Malbrough, Hollis, and Parker. The testimony established, however, that Detective Catano made it clear that he was not asking or ordering Edwards to open the package. There is no evidence that Edwards felt she was obligated to open the package. We conclude therefore that the government’s knowledge and acquiescence, when considered in light of Catano’s communication to Edwards that the decision was her’s alone to make, did not make Edwards a government agent for the purposes of the Fourth Amendment. Cf. United States v. Kinney, 953 F.2d 863, 865 (4th Cir.1992); United States v. Feffer, 831 F.2d 734, 739 (7th Cir.1987); Gold v. United States, 378 F.2d 588 (9th Cir.1967).
With respect to the question of intent, the district court found that Edwards’s decision to inspect the package, even if accompanied by a dual motive of assisting the officers, was motivated by her obligation to ensure that her employer was not being used as a means of carrying contraband. As the Supreme Court has pointed out, a commercial carrier such as FedEx has a “duty to refrain from carrying contraband,” and such a carrier’s employees may act to ensure compliance with that duty. Illinois v. Andreas, 463 U.S. 765, 769 n. 1, 103 S.Ct. 3319, 77 L.Ed.2d 1003 (1983). That a private citizen is motivated in part by a desire to aid law enforcement does not in and of itself transform her into a government agent. Malbrough, 922 F.2d at 461-62 (holding that informant who trespassed with the intent to find out if marijuana was being grown was not a government agent for the purposes of the Fourth Amendment); see also Coolidge v. New Hampshire, 403 U.S. 443, 488, 91 S.Ct. 2022, 29 L.Ed.2d 564 (1971) (“[I]t is no part of the policy underlying the Fourth and Fourteenth Amendments to discourage citizens from aiding to the utmost of their ability in the apprehension of criminals.”). Given the absence of evidence that Edwards was motivated solely or even primarily by the intent to aid the officers, we conclude that the district court’s factual finding that she opened the package out of her desire to ensure that her company was not being *706used as a vehicle in the drug trade was not clearly erroneous. Thus, the district court did not err in denying the motion to suppress.
II.
We next consider Smith’s argument that the district court erred in permitting certain rebuttal testimony. After the government rested its case-in-chief, it became aware of a potential rebuttal witness, Delores Schmidt. In an interview, Schmidt stated that she knew a man named “Sergio,” with whom she had conducted numerous drug transactions. Believing that “Sergio” was actually Smith, the government desired to offer Schmidt’s testimony under Fed. R. Evid 404(b) to rebut Smith’s claim that the package of drugs had been mistakenly shipped to him.
Smith contends first that the district court erroneously permitted Schmidt to testify under Rule 404(b). We review de novo the district court’s interpretation and application of the rules of evidence, and review for an abuse of discretion the factual findings supporting its evidentiary ruling. United States v. Blue Bird, 372 F.3d 989, 993 (8th Cir.2004). Because Rule 404(b) is a rule of inclusion, we presume that evidence of “other crimes, acts, or wrongs” is admissible to prove motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident, unless the party seeking its exclusion can demonstrate that it serves only to prove the defendant’s criminal disposition. United States v. Campa-Fabela, 210 F.3d 837, 840 (8th Cir.2000). Other crimes evidence is admissible if it is relevant to a material issue, the other crimes are similar and reasonably close in time to the charged crime, the evidence is sufficient to support a jury’s finding that the defendant committed the other crimes, and the probative value of the evidence is not substantially outweighed by unfair prejudice. United States v. Carroll, 207 F.3d 465, 469 n. 2 (8th Cir.2000). Schmidt’s testimony satisfies the first of Carroll’s requirements: it was clearly relevant to a material issue (Smith’s knowledge of drug dealing), it concerned events that were similar in kind and close in time to the charged crime, and it was sufficient to support a jury determination that Smith was involved in drug transactions with Schmidt.
With respect to the question of unfair prejudice, there was little chance that the jury would misuse the testimony in light of the instruction limiting its consideration to the issues of knowledge and mistake — two proper uses of other crimes evidence and two issues made relevant by Smith’s defense. Lothridge, 332 F.3d at 504. Smith argues, however, that he suffered unfair prejudice because he was not given reasonable notice before trial of the government’s intention to introduce Schmidt’s testimony. Rule 404(b) provides, in pertinent part, that “the prosecution ... shall provide reasonable notice in advance of trial, or during trial if the court excuses pretrial notice on good cause shown .... ” Essentially, Smith argues that the district court improperly concluded that the government’s explanation— that it simply did not have actual knowledge of the existence of Schmidt’s proffer — satisfied the good cause requirement of the Rule.
There has been no allegation that the government intentionally withheld notice from Smith or his attorney. Rather, it appears from the record that Schmidt’s proffer was obtained and filed independently of the investigation of Smith. It was only after Schmidt’s reference to “Sergio” was matched with Smith’s self-identification as “Sergio” when receiving the FedEx package that the government real*707ized that her testimony might be relevant to Smith’s trial. The government immediately informed Smith’s attorney of Schmidt’s proffer, and he was given access to question her. Smith argues that, not withstanding the government’s prompt notice, he was unfairly prejudiced because his theory of the case, which his attorney outlined to the jury during his opening statement, was vitiated by her testimony. He maintains he was faced with a “Hob-son’s choice” or “Catch-22” situation, unfairly forcing him to choose between continuing with his theory of the case and attempting to minimize the damage of Schmidt’s testimony or else changing his theory of the case and risking the ire of the jury for failing to deliver on the representations he made in his opening statement.
We conclude that the district court did not abuse its discretion in concluding that the government had demonstrated good cause for its failure to disclose Schmidt’s testimony. In a perfect world, the government would have been aware of, and would have disclosed, her proffer earlier. But we do not live in a perfect world, and a criminal defendant is not guaranteed a perfect trial, just a fair one. United States v. Flores, 73 F.3d 826, 832-33 (8th Cir.1996) (quoting Bruton v. United States, 391 U.S. 123, 135, 88 S.Ct. 1620, 20 L.Ed.2d 476 (1968)). The discovery of Schmidt’s proffer was “simply one of those unexpected developments that occurs in the course of a trial.” Id. at 832. The unexpected development did require Smith and his attorney to make some difficult strategic decisions in the midst of trial, but that defendants are faced with such decisions at inopportune times does not necessarily require the exclusion of evidence. United States v. Spence, 125 F.3d 1192, 1194 (8th Cir.1997) (holding that the district court’s decision to defer ruling on a motion to exclude “other crimes” evidence until the middle of the trial was not an abuse of discretion despite the fact that it potentially required defendant to adapt his trial strategy accordingly)-
The judgment is affirmed.
. The Honorable Richard G. Kopf, Chief Judge, United States District Court for the District of Nebraska.
. The Honorable David L. Piester, United States Magistrate Judge for the District of Nebraska.