*sigh* Yea, people are VERY ignorant.
A few weeks ago I was looking at fish and this little girl (about 12 or so) asked a worker "do you all sell algae eaters? I'm not sure what they're called... but they're black." Upon that, the worker took the child to the common pleco tank, and she exclaimed that's what she was looking for. I casually walked over, but stuck my nose in their business as the pleco was being bagged. I mentioned that they can get 2 feet long, and the girl said "wow, really?" as she took the fish and bought it. You know she owns a 10G probably. I have nothing to base that on, but I feel right in saying that there's a 95% chance that pleco went in a 10G.
I would love to own a fish store, and if I did, the tropical and marine fish would be in separate rooms, and the small and large fish would be in separate rooms. Every single tank would hold one species (not 50 fish of 3 different species in a single tank) and every tank would be labeled with a common name, latin name, diet info, adult length, level of aggression, and other tid bits. There would be a huge book at the store entrance full of pictures, info, and descriptions of every fish in my store, and even ones I don't have. IMHO every store that sells fish (be it a pet store or walmart) should have this set up, or something similar. This would reduce poor purchasing by so much. Hopefully people think twice when information is shoved in their face.
Sorry to get on such a role, but human ignorance really fires me up.