I would just give the money back. I am assuming you are referring to a fairly short amount of time. like less than a month or two.
I just purchased a rabbit and was told it was a doe and now we think it is a buck. I know it happens, but we were more dissappointed than anything. The thing is we aren't positive. My father n' law a veterinarian, and raising rabbits for 60 years, wasn't even positive. 3 1/2 months old. so frustrating. This got me thinking about the ethics of it and what we will need to do. Since we are going to try to raise Silver Fox rabbits.