depends what size your tank/wallet is?
Personally i dont think fish that can attain a reasonable size should be freely offered for sale.
Well, you'd need to examine every species' ultimate size and guess what size of tank it needed?
What I think is unreasonable?
Sharks, all species including Chiloscyllium, large Pangassius species, large Pimelodella, Sepia officinalis (gasp) LOL etc etc
can you be more specific clown? I have seen home aquariums at 20 odd foot long!