An Oklahoma gun vendor, set up at a weekend gun show in Oklahoma City, was passing a handgun to a potential buyer when the gun discharged. The dealer did not realize there was a bullet still in the chamber of the gun. The dealer's teenage son was shot in the leg.
Police check guns at the door of the event to make sure they are unloaded and properly marked, but they do not check guns sold by vendors.
It should be noted that the handgun in question was from the dealer's private, personally owned collection. This means there would be no criminal background check run on the buyer.