I frequent both Petsmart and my family-owned LFS. I just like to watch all the fish, even if I can't own them... and I like to watch the fish I am thinking of buying for a long time to get to know their behavior and imagine how they will be in my tank, and as others have said give time for illness and such to be apparent before I buy.
In Champaign, IL we are fortunate to have a pretty knowledgeable daytime staff at PETSMART (never been there at night) who are all die hard hobbyists themselves. If they tell you something wrong it is not because they don't care, but just that they haven't come across that info yet. As another poster said I get WAY better info here and online than at either of my LFSs anyway.
I LOVE SAILFIN our family-owned store. Nearly everyone there is very knowledgeable and they work to make sure the new people learn to value being knowledgeable even if they don't know things yet. Employees will say things like, "go talk to so-and-so, I should have learned more about plants (rainbows, cichlids, saltwater, etc) by now, but he/she is an expert on that."
I think the biggest difference between the two though, is that Sailfin stands behind their fish. If a fish dies within seven days (or sometimes longer if they know you and your dedication to the hobby well) they will replace or refund it. If you decide to return a fish at anytime for any reason they will give you a % of the cost of the fish as a credit... no receipt, no questions asked.
Plus they have a much better selection if you like more rare fish, or beyond the basic species of any one fish (they often have five or more different types of corys for instance, and always a good selection of Killis, Rainbows and Cichlids). They are the only local Saltwater and Koi store around.