The pet shop I get my fish from know the names of their fish and have all tanks labeled.
However, back in my noob days, I used to buy fish from market merchants. Or more like my dad used to buy them, few things I've bought from there myself: two swordtails.
But what my dad has bought was either:
a) Mislabeled
Corydoras, hoplos and fossilis were labeled as "cleaner fish", although for the fos, they also mentioned what it was.
b) Lack of info on their care.
Not only was the fossilis poisonous, the hoplos grew huge and i wasn't even supposed to keep them in a 40L tank, but also dad bought 4 fantail goldfish (1 black moor, 2 silver and 1 gold fantail) which made my water stink, never grew much, lived only 4 years in that 40L with the rest of the fish soup I had.