I don't think it matters what context it was said in. Lets give him the benefit and say that he simply asked "Could I give you 25 bucks for it, that's all I have."
The shop keep, whether the owner, manager, or just a clerk should have responded differently. I would have been insulted too. I think customer service has taken a turn for the worst no matter if you're a hole in the wall LFS or a Barney's. I don't go to places where I get bad service. Not restaurants, shops or LFSs. I can spend my money elsewhere, where I get a good price and service too. There are enough places around, that I can go elsewhere. The lady at the shop should realize she doesn't have a monopoly on fish and she will lose customers.
Also, that fish was too much, IMO. I just bought my fuzzy dwarf for 19 bucks. Good health, striking color. Has been great. Bought at an LFS, not online or anything like that.