Amen on gunshop owners treating you like you're incompetent fools. Had one get into a fight with me the other day when I went in inquiring about local gunsmith (should have been a tip off to me when he said he didn't know of a gunsmith in the area). The owner of this particular shop, besides for deriding me for purchasing a RRA carbine and informing me that 'if its not colt its excrement' and that 'the DEA would NEVER contract for a M16/AR15 platform from anyone other than colt' told me that one could not convert a post ban-rifle into a non-ban rifle. When I probed him on the reason for this, he proceeded to spew forth a haphazard and illogical parsing of tasty tidbits and juicy morsels of the entire scope of federal firearms law, none of which happened to be a correct or complete interpretation of any of the USC provisions which he was referring to. It was quite clear from his general rambling that he was confusing not only 922(r), the 1989 ban, the 1994 ban, and the NFA but several other provisions as well. After pointing this all out, he indignantly asked "well, what are you, a lawyer?" Which, I happily obliged him with my card.
Anywho, this is really neither here nor there. But, I've always found it much better to be well prepared with your own facts and research before you go into any local gunshop looking for info. I've found that the tactical advantage of letting them think you're not familiar with things does work out in your favor in the end as you can catch them in inaccuracies.
Moral of the story? Unless you are friends on a personal basis with the owner/dealer, be wary of the cornicopia of verbal excrement and yarns that local dealers will spin for you.