I have to say the PetSmart by me has a broad spectrum of knowledge in the fish dept employees. The mor I learn here the better I am getting at figuring out which employees I will talk to and which I won't. The have one young girl about 18-19 or so I would guess, who gets a deer in the headlights look for every question that we have ever asked. But at least she doesn't offer information she doesn't know. I have had a few others tell me bad information I have come to find out later, particularly about which fish can live with which others, and they say things with such authority I believe them. I have also found there are one or two people at my PetSmart that really do seem to know what they are talking about, so if I have questions now I try to deal only with them.
I am rapidly learning that the best way, as said before, is to do your research and get to know the stores in your area to figure out who to listen to and who not to. I am still a total newbie and am still probably going to listen to bad advice again somewhere along the way, but this site is helping me a lot!