When I sell a gun this is the "talk" I give to every single buyer:

"Let me explain how this works. I'm going to sell you this gun. I'm going to take your money, ring it up, and give you a receipt. You bought it. Its yours. However, you cannot take possession of this gun you just bought unless the FBI says so. I'll take this information you filled out on the 4473, enter it into the NICS database, and the FBI will give me one of three responses. A tab will pop up that says "proceed". That means we're done in five minutes and you can have your gun. Another tab can open up that says "delay". They do not tell me why. I cannot ask why. The FBI has three business days to deny the purchase or the firearm is transferred based on their not responding. I can get a tab that says "deny". The FBI has refused your purchasing or possessing this or any other firearm. In this case we will refund the purchase amount less $50 to cover our time and expense. You may appeal the refusal to the FBI. They denied you - we didn't. Do you understand?"