you are dealing with state law issues that vary state to state. I can give you the VA answer. Are you a horse professional ? Did you represent yourself as a horse professional ? If the answers to those questions are No, and ur not a dealer or pro trainer, then all horse sales in VA are as is with no warranty unless a written one is added. So unless they have a written guarantee ahead of time then the default ruling would be no refunds.
I got into this over a partially blind appaloosa horse. I advertised it as partially blind. I signed release for buyers to talk to my vet. I gave them a 30 day at my house trial period, they didnt take advantage of. I only sold horse for 500 , back when she woulda been worth several thousand if she wasnt blind. Same thing they wanted their money back cause she ran into things,, Well duh you bought a blind horse. They sent certified letter gettign snotty, I sent them a copy of the original add stating horse was blind, as well as a copy of the above mentioned state law.