Twice over the last 40+ years, I've been in a gun store and someone came in with an "unloaded" gun that had one or more rounds in the chamber. The first one was back in the late '70's, a guy came into the store near my house with a Beretta 92. He tells the clerk he wants to sell it. The clerk asked him, "Is it unloaded?", and he said, "Of course!". The clerk pops the mag out and then racks the slide back and a round pops out and hits the glass counter very loudly. "Oh Jesus!" the customer says. The clerk looked at me like, "See what morons I deal with?".
The second time, some guy comes in with a nasty looking old Ruger P89 and it's not only loaded, it was fully loaded, a full mag and one in the chamber. It was a very old guy and he says, "Oh boy, I thought it was empty!". I wanted to ask him,. "Why would you think that?". Just the weight of it should have given him a clue. I think half the reason they offered him as much as they did was to get it away from him before he cranked a round off "by surprise". He walked out with some cash and no gun. That gun was in their used case marked at exactly the same price they gave him for about a year, and suddenly it was gone.