Having previously worked at an LFS I have heard most of these misconceptions, what surprises me is how little people can know about standard biology. My favorite has to be how "shocked" people are when their misconceptions are corrected.
I once had a customer, a middle aged lady asking which of these fish can be put in a bowl. After explaining that bettas are the only fish we have that could be kept in bowls (after explaining that no fish actually should be kept in a bowl), she kept on asking "can I put that one" pointing at several species of other fish.
At last she pointed at the RBP's we had and asked "What type of fish is this?". After my reply she actually got angry because we are keeping dangerous, illegal animals (no fish are illegal here). A couple seconds later she just stormed out.