I once had a clerk hand me a semi across the counter - muzzle first without ever checking that it was clear. That was when I lost all of my manners and made it very clear that he had no way of knowing whether it was a loaded weapon, etc., etc. As it turned out, his boss was watching the entire episode - he came over and chewed him out after I finished and took over for he clerk. He actually thanked me for helping to "train" his clerk.
Just be courteous and you'll be fine. If I'm going to purchase a handgun - semi or revolver - most experienced clerks expect you to cycle the slide, test the timeing on a revolver, etc. I just ask first - after all - it's not my handgun at that point. If you are a first time buyer . . . even though you've don your research . . . tell 'em. Usually a knowledgeable clerk will go out of their way to not only demonstrate but allow you to do the same in regards to cycling, checking timing, etc.
Good luck in your search - you'll do just fine.