This does not exactly qualify but it is on-topic: One of my first jobs was at Petco. My first day on the job I didn't know dick about fish and I sold a lady a bunch of African chichlids (the small, colorful kind). The fish of course killed everything in her tank as soon as she got them home. Oops.
Don't trust fish store people working at the big chains. There is no "training" you learn over time (meaning you tell lots of customers wrong or stupid info before you learn better)
LOL I still laugh about it when I think of my then-manager telling me I sold a bunch of fish to a lady; and those fish killed alll of her existing fish lol
Don't be too hard on fish store employees. Do you have any idea how much money they make? Practically nothing. What is their motivation for being educated about fish (or anything, for that matter)???