Dropping the slide on an empty chamber, snapping a revolver cylinder closed with a flick of the wrist, slap snap and dry-fire, and likewise antics cause damage to firearms. With the price of a good gun getting onward to that of a thousand spot, it's quite an investment to damage out of hollywood ignorance. I get pretty annoyed when someone abuses one of my guns gangsta style. It's not cool, and only shows how much a person does not know.
The proper way to handle a firearm in a gun shop is to remove the magazine, and lock the slide to the rear, inspect it to ensure it's unloaded, then if you may gently close the slide. Re-lock the slide to the rear when handing the gun back to the owner, be safe. And don't dry fire another person's weapon. Some guns are more or less prone to breakage by dry firing. Even manufactures who say it's ok to dry fire, it's still not good for the weapon. Ruger confirms dry firing is OK in their revolvers, it's written right in the users manual, however, my single six firing pin broke after dry firing it perhaps 20 times.
I'm not trying to be too critical, but many people are very particular about their guns, I am.