@Live_Wire, I saw where you said this was the second horse the buyer had sent back to you.
In my opinion, there are some problem buyers out there. No matter what horse they purchase, there is going to be a major, unsolvable issue within less than a year of ownership. From what I have seen, it is usually the buyer and not the horse.
I have actually known buyers like this, and had them look at a horse I had for sale. I had them come before the horse had been groomed and tacked. She had the audacity to spray his face with fly spray, right in the face, and complain that the horse took half a step sideways. I knew at that point she was going to be an issue- not the horse.
Eventually, she bought a very nice quarter horse from a very reputable dealer in our area. This “dealer”, brings in horses from out west and resells them in the Northeast. Very nice horses, mostly registered, broke, some with even AQHA points. By no means inexpensive horses.
If I remember correctly, she went through a total of 4 horses. She kept 2 and sent 2 back to the dealer. One was sent back because it spooked when a bear ran out in front of it! A bear!!!
After hearing that, I was glad I decided to keep the horse I showed her. I put him down at age 24 due to a neurological problem, but he and I had 20 wonderful years together.
I would have no issues selling the horse. She was for sale when they bought her, and I would think they would have to understand you would not be keeping her.
But just a little advice- these people sound like they have chronic issues with the horses they choose to purchase. I would recommend not doing any future business with them.