is it the same store you got them from? How long have you had them for?
with me, I tell my LFS that I bought the fish, and I realized I made a mistake, I'd like to return them for what I paid for and get something else. Sometimes they'll agree, sometimes they wont, but let me put the credit to another fish.
Since salt fish has no guarantee, and most places wont take it back at all, it can be a 'better than nothing' deal.