I think this is an interesting issue. The last place I lived had quite a few comic book stores, and over the years I ended up categorizing them based on how close to the Android's Dungeon they were. Here in South Bend there is only one store, and it falls into the awesome category.
It seems like a lot of the people in here aren't exactly talking about the same things. I think there is a difference between a customer, and someone wanting to sell their crap to the store.
If someone comes into a shop with a legitimate interest in comics, even if it is just buying a gift for someone, then talking down to them is idiotic. Yes, people who don't know about the books might ask dumb questions, but explaining things to them in a polite way will get you their money, and possibly get them interested in comics. Trying to shove Fables and Sandman down the throats of female customers because they are 'girl comics', for example, is an insulting and outdated mode of thinking.
If someone comes into the store with a box of Spawn #1 and thinks they are going to get thousands for it then I don't think there is the need to treat them so delicately, unless they are a parent selling their dead kid's collection or something.
I have encountered 4 or 5 Comic Book Guys over the years, and I stopped shopping at their stores. If I ask you which GI Joe book currently running is canon I don't need attitude along with my answer.