Reef job , where i work we dont sell any fish that we dont think will co exist with the other fish its going to live with . yes we lose sales but we keep customers by always using the correct advise regardless of how bad they want it .
i think your talking about petco or some other chain store and if not they are simply jerks for not asking . we dont sell fish to become a meal where i work and people never question our authority but rather respect it .
we even have a store nearby that runs great sales on fish that just came in yesterday and have ick on them and people wonder why their tank is messed up . its not from our doing i must say .