that's why you always- always- talk to the oldest guy in the building- the guy with grease under his fingernails that just carries himself like a guy who knows what he's talking about. he will generally be about 40 years old, have a mustache, and have a bunch of pens in his shirt pocket. most places have at least one of these guys, and if they don't go to the place across town that does.
also, avoid the chains whenever possible and go with a locally owned store where the owner and/or his wife are probably working the counter and- these places will usually be a little "grittier" than the chain stores.. NAPA and Carquest are the exceptions to this rule in this area. they are usually good.