aThere is no national database for stolen guns.
You can call the local PD or Sheriff and have them run the S/N against the local list of stolen weapons.
Just ask for ID and a Bill of sale, like you would do when buying a used car.
Basically CYA to the extent you need to feel comfortable with the transaction.
Karl;
I tried asking for a receipt on one gun I traded off a member (pre FFL) and it was a trade of a trade of a trade issue. From what I read going on with some members on InGun people keep a gun a few weeks and trade it off for something different.
I ask for a drivers license which I copy and file on EVERYONE I deal with, no exceptions. Due to liability issues I will not sell or do a transfer to/for anyone I am not 100% comfortable with. If they don't want to show me their ID they can go to Gander Mountain or some other large company who have deeper pockets than me. This goes for all purchases; they have to do it at WalMart if they pay with a check so why not for the private gun dealer.