You need to take them to your local fish club's sales instead of the LFS Harlequins. I find that my common guppy fry, all grown up, fetch a price that more than pays for their keeping when I sell them at a club auction. On the other hand, a dedicated local fish shop, that is well known for selling rare and hard to find fish, do not give me much at all for fish, and it is always in terms of store credit, not cash. The heck with that. I sell my surplus at club auctions for my own club and others. I will never make enough to pay for the hobby, but I refuse to give away the fish I have spent the effort to raise.