I guess it's too much to ask for a sales person to know about the products he sells? It is sad, Krochus. I too have been to car dealers only to find out I have learned more about the vehicle by spending 5 minutes online, on a website, than the sales rep knows about it. It really kind of ticks me off.
The same does seem to hold true about gun dealers. Many times they have uneducated people behind the counter. (By uneducated, I mean about the products they sell, not just "University" guys, although guns are pretty technical machines)
It is almost easier, sadly, that one can learn more from the internet (although you must be careful in what you read) than you can from spending some time in a gun shop.
Believe me, it hurts to admit that. I have always loved just hanging out in gun shops, soaking up the, well, BS mostly, but you can learn a thing or two in a good shop.
These days, people are just looking for a paycheck, and don't really care about anything else, be it product or customer.
Atomic Chicken, as others have said, it may have been prudent to ask to disassemble the pistols directly. Some folks aren't very deductive. However, for the clerk, there are definately better ways to handle a situation than what you experienced. The "manager type person" should also have taken control of this situation, by trying to resolve it, taking over, etc.
If you frequent this shop, and generally like the service, prices, etc., I would give them a second chance. IF that particular person still works there, the best thing to do would be to attempt to educate that person on firearms, if possible. Maybe someone else will benifit from it. Apparently the sales person should, with his limited knowledge. If not, just don't use that person for anything, ask for someone else. If you feel very strongly about it, talk to a manager about your experience.
If you won't miss the place, let your money talk, and don't spend it there, thats easy.