It's a story we have heard before. Took out his personal gun (Kimber .45) to show to a customer, removed the mag but (you guessed it) failed to clear the chamber.
First rule he broke was the obvious "Always treat every weapon as being loaded". Second rule broken was that no loaded weapons are allowed at the gun show. No serious injuries, but that could have been a nightmare. Gives the rest of us a bad name. I don't think he will be welcome at anymore RK gun shows!
I know a guy who bought a collection from a deceased fellows family.
They inspected all of the rifles to insure that they were unloaded and put them out on display.
A month later a customer picked up one of the rifles opened the bolt, and a live round flew out!
I see people pick up guns all the time in situations like that and just pull the trigger.