Okay, JimmyR, now look at this from the seller's perspective. Let's assume that he has done nothing wrong, but might be in possession of a firearm that might have been stolen before it came into his possession. You want to limit your potential losses. What's in your proposal for the seller?
Suppose you meet him at a police station, the police run the serial number, and the gun turns out to be stolen. The police confiscate the gun on the spot. You do your little happy dance because you were saved from buying a "hot" firearm. Meanwhile, the seller is standing there without his firearm AND without any compensation for it. Are you willing to pay him half the asking price in order to compensate him for sharing the risk of having the serial number run? THAT would be the fair and ethical thing to do, IMHO, if you are concerned that the gun might be stolen. Why should the seller assume ALL the risk of protecting you?
In the insurance business this is called "risk allocation." You are being selfish and asking the seller to assume all the risk of protecting you from what you perceive as a risk. That's not reasonable.