I think it might be a little late for that guy but my kids can regurgitate these by heart:
1) treat every firearm as it were loaded... (Hey guess what this one was loaded)
2) never point your weapon at anything you do not wish to destroy (I think a customers backside would qualify here)
3) keep your trigger finger straight along the frame until you are on target and are ready to fire (obviously his was not)
4) be aware of your target and its surroundings!!!
Violate 1 you might get lucky, violate 2 and the poopy is going to hit the fan!!!
If I had a dollar for every weapon that was ND I'd be 13 dollars richer.
That's what they always say " I swear, I checked the gun, and it was empty." STRIP OUT! LOOK AND TOUCH....
A weapon is not clear if you still have a mag in it, your looking for that one round in the chamber!!!!!!!