Just a word to the wise... I'll buy from a pawn shop with a receipt and form 4473, but unless I know the proprietor to be an honest guy, I'd NEVER sell or trade a serialized gun in a pawn shop.
There was a pawn shop in central Maine that I used to keep an eye on, but never bought from. They were really twitchy and the shop was filled with cheesy repop swords, leather wear, water pipes and fantasy blades. The owner kinda gave me the creeps, but there were other shops around so driving by I would invest 2 minutes to look in his cases. One day about five years ago, the ATF popped him. The story goes that he was buying guns from the public and only some of them were actually going on his books. Seems he had some connections in New Jersey and the "good stuff", mostly black guns, were whisked away and sold undocumented on the black market there.
I pity anyone who sold a legally owned, serialized gun to them and did not keep a receipt. If that gun is picked up at a crime scene and forward traced, that seller is going to have alot of explaining to do...
Be careful.