I had a reverse issue. I sold a male a while back that turned out to be a female. The buyer was actually quiet happy about it but still offered her back to me if I wished saying that he would take a male. In talking with him I found that he was willing to trade because he thought it was unfair to me even though he would prefer a female as he bought "him" (lol) because he was a very pretty male. I told him not to worry about it due to it being my fault. It taught me to re-sex my animals at least 3 or 4 times before even considering selling them, as well as two more once I find a buyer.