I think that when a dealer (FFL licensee) receives a gun, whether by purchase or consignment, he is required to enter it into his log book. When he disposes of the gun he has to enter into his log book the disposition of that gun. So he either has to log it out to another FFL licensee or run a NICS check and have the form on file. I don't see how he can simply hand it back to the previous owner with no paperwork. I can find no ATF regulation to the contrary.