It's funny you mentioned this as I have recently wondered what the potential was for some "customer" that meant to cause trouble for the shop or just see his "handy-work" on the news to "slip" a round in a firearm after checking it out and handing it back to the clerk. That's why I guess it's a good idea to check it both when you hand it to them and when they hand it back.
There's a shop near where I live that will pull two or three guns out on the counter, walk into the back room to check on another or talk with another customer with the guns still out, take them back after you inspect them and then place them right back into the case without checking. That's asking for trouble, IMHO.
