I have bought and sold guns using forums. My personal experience is if I'm selling, I use paypal FF. I then keep the money in paypal until the FFL on their end receives the gun and the buyer looks it over and is completely satisfied. then after getting an ok from them, I then transfer the money from paypal to my account. If there not satisfied for whatever reason, I then keep the money in paypal until the gun is returned then wire their money back to them. I've never had to actually do that but it's a complete honor system. Word gets around fast if you are shady buyer or seller.