The guy probably bought it because he thought if he put it down it would be sold in an hour.

We are all assuming that the guy who bought the gun would want to hear it might be a salt gun. He might have been angry at you for telling him the bad news. He also might have thought you were sorry for putting it down and was hoping the bad news would make him walk away so you could buy it. I've seen it happen.

Generalities do not fit every situation. Even the ones that many on this board live by. Your best bet in this situation was what you did.

So many guns, so little time!