I see a lot of frivolous lawsuits relating to consulting business. If refusing a sale, one does open up the gun shop to spurious claims of illegal discrimination or bias (real reason was because they were gay or black or a different religion, etc.) There should perhaps be due care to protect against these lawsuits when refusing sales. Steps like: 1. Discuss the possibility of refusing the sale with management. Make sure someone writes down the reasons why refusing the sale is being considered: suspicion of drug use, suspicion of straw purchase, suspicion of likely illegal or violent use. Simply document suspicion, not the reasons for the suspicion. Reasons for suspicions can often be portrayed as illegal biases. Try and forget the reasons for the suspicions quickly after the event, and honestly answer "I do not remember" if ever asked about it. 2. Call BATFE or a local law enforcement agency while considering the sale. Tell them your suspicions and ask for their advice regarding the sale. They will almost always advise against the sale. Your real reason for denying the sale should be following their advice in the specific situation. 3. Follow up the refusal of the sale with a report to BATFE and/or local law enforcement with as much info as you have as well as with your suspicions. Suspicions that are quickly reported to law enforcement are much harder to portray as an illegal bias. Be sure to only report your suspicions (NOT the reasons why), because the law enforcement will probably document everything you report to them, and if you give reasons for your suspicions, they may later be portrayed by the plaintiff's lawyers as evidence of illegal bias. Of course, all these considerations also apply to private sellers who may choose to refuse a sale based on suspicious appearance of behavior.