Wow, I can't believe they won't sell you that fish. When I worked at a pet store in charge of the fish department I would sell those fish in a heartbeat, only fish I wouldn't sell was our archer fish display tank or the blood parrot that was mangled by a red devil (the parrot cichlid became a store pet), I've had people drop off monstrous oscars, arowanas, red tail catfish, etc. and I would have them for sale for something like $200 but I'd have people offer me $50 and I'd take it, one less mouth to feed and I have another spot for a fish to sell. I'm going to have to agree with others though, show them pictures of your tank and offer them a few hundred dollars. You could also say if you don't sell me the fish, I'll post this on facebook so others can see how bad the conditions of your fish tanks are.