The background check on private sales can be a PITA because the NICS doesn't always clear you immeidately. I get delayed every time.
So if I go to a gun show and want to buy a used gun from you we find an FFL who isn't busy and ask him to do the transfer. Well it comes back delayed. So what do we do now.
Do I pay you for your gun and leave it with the dealer until cleared? If the dealer is a substantial drive from where I live I have to make quite a drive to go pick it up.
Do you keep the gun, I keep the money, and then when the NICS comes back clean we both have to drive to the dealer?
I'm not talking about the guy with a table full of guns that sells them show after show.