Considering they get paid close to minimum wage and get hired off the street you can't really expect them to be marine biologists. Once they have worked there for a while or if they have kept fish for some time at home they get better, but I have personally never listened to anything they say at chain pet stores and a few times I was compelled to contradict them when the advise they gave to other customers was just too much for me to ignore. But you get what you pay for. Employees at pet chain stores are rarely experts. But that said they do try and sometimes you run into a knowledgeable person. Your best bet, however, is to do the research before you go out and buy a fish and if you still have some questions ask easy ones first that you know the answer to. If you get the right answer you might ask for the more complicated stuff you don't know yourself but you still take a chance that you are expecting more that you will get.
20g L46/hastatus/pygmy corys, 10g OEBTs, 10g blue bees/blue velvet shrimp, 10g CRS, 15g L174s, 10g yellow shrimp, 15g clown plecos/L340 fry, 25g L134s/CPDs, 29g Weitzmani/panda corys, 46g L134s/salt and pepper corys/BNs, rubberlip pleco, 55g SAE/L201s/L199s/BNs/kissing gourami, 75g L316s/BNs/old fish folk, 30g L340s/L211s/CPDs/micro rasboras,10g tangerine tiger/snowball shrimp, 20g L134/habrosus corys, 10g CPD fry