You want to know why I'm a little OCD when it comes to chamber checks on firearms? Allow me to share a story:
At the first gun shop at which I worked, which was also a pawn shop, we had a relationship with a pawn shop owner down in the city. Every few months, he'd drive out to see us with a briefcase containing a few old Colt Police Positives and Smith .38/.32 Terriers and Browning Vest Pockets and suchlike and we would swap him a big box of Lorcins and Hi-Points and Jennings and cash to make up the difference.
One time he came up, the sticking point in the negotiations was a PPK, an early Interarms-marked stainless example. Initially he was thinking about keeping it. Then he wanted too much for it. Then he relented and we added it to our side of the pile.
He handed the Walther to me, and I locked the slide back and checked the chamber, and passed it to a coworker over at the computer. She printed a trigger tag out for it and handed it, slide still locked back, to one of the other salespeople, who put it in the showcase.
Then our buddy the pawn shop owner crawfished. I sighed and pulled the gun from the showcase, removed the trigger tag, and laid it on the counter between him and my boss. About the time pawn shop guy was leaving, I was walking out of the store to cross the street and get lunch for everybody.
When I came back, there was the PPK, sitting on the counter by the computer. "Arthur changed his mind again?" I asked, and was told that, indeed, he had sat in his car for a moment and then came back in and threw the Walther in on the deal at the last minute. Sweet! I still had the trigger tag handy, so I put it back on the gun and passed it to the salesman who put it back in the showcase with one hand while eating his hamburger with the other.
I wandered off to a far corner of the showroom where I could eat my burger in peace, back turned to the sales floor, when *KA-BAM!*
A customer is standing there with the PPK in his hand and an appalled look on his face, smoke wisping theatrically from the barrel and a divot in the linoleum at his feet containing a flattened Winchester Silvertip.
That's right, Arthur had loaded the PPK back up in his car, and then brought it back in to add to the trade, and not one person who handled it from the time I picked it up and put the trigger tag on it to the time the customer made the loud noise had bothered to inspect the chamber because, hey, we had already done that when he brought it in the first time, right?
Lesson learned: I don't care if I set the gun down and just look away for a second; that gun gets checked again when I pick it up. Period. Unless it has been in my field of vision the whole time, I don't know what might have happened to it while I wasn't paying attention.