I witnessed this happening in Pensacola. A dealer handed a customer his carry gun, after "unloading" it by removing the mag. The customer pulled the trigger while holding the gun sideways. It hit a man 10 yards away in the arm. Place went quiet, then went back to business as the interested parties were removed.
The cops came and arrested the dealer/gun owner - as it should be. The responsibility for the proper unloading and safe handling of a firearm rests with the owner. I don't expect anyone else to know how to unload a P7 or a Webley - there are too many guns to assume anyone "knows better" - especially in a room full of first time buyers.