I agree with Dan - which is why all of my fish purchases now come from a single LFS - the guys that are in the shop have come to know me and my husband and are quite familiar with my tank. If they know something, they pipe up. If they don't, they grab one of the many books they have behind the counter.

It's really an all around nice store, and I'm lucky to have found it! (If you're in the SE Michigan area - I highly recommend them - It's called "The Fish Tank" in Westland, MI.)
As for the bigger stores - I'm starting to feel for the employees. Some of them really do care and they try - but how are they supposed to help educate customers when they have a manager breathing down their neck to make the sale?
But I do have my limitations as well. My local PetSmart is great - but there's a guy that works there who, quite literally, thinks he knows more about fish than anyone else. While, granted, he does know quite a bit - he doesn't need to get a cocky attitude with the customers, regardless of their knowledge level. For quite a while, before I found my now favorite LFS, I'd buy my fish from PetSmart (Hey, I've never had a problem with their fish!) and each time I saw this guy in, I'd just leave.
He was bad. It wasn't that he was offering advice (most of which was basic) when you'd get your fish, it was just the WAY he was offering the advice. He'd say it with this condescending tone, all the while hurriedly rushing the sale along. My end impression is that he just came to hate his job. Hopefully he didn't come to hate his fish tanks too.

(He kept several, smaller, tanks at home)