I'm sorry this happened, but take a lesson from it. When someone looks at a sale horse, if they really want that horse, they need to put down a non-refundable deposit. Too many people are just 'hoof kickers' and say they want a horse, or will have a vet check it and then disappear, never to be seen again. If a seller takes them at their word and turns down cash in hand, they may lose the sale forever.
When I sell a horse, the ONLY way I will take it off the sales list and not sell it is if the first person leaves a 25% non-refundable deposit on the horse. If they schedule a PPE and the horse fails the deposit is, of course, refunded immediately if they don't want the horse after that. Otherwise, if they just change their mind, then at least I haven't lost everything. When I take a deposit, I write up a contract showing that "so and so agrees to purchase XXXX horse for $XXX, of which 25% has been placed as a non-refundable deposit. Horse is scheduled to have a PPE done not later than XXX Date, and if passes sale is to be completed and paid in full on XXX date. If horse should fail the PPE and buyer declines horse for that reason only, the deposit will be refunded. Horse is bought "AS IS, WHERE IS" with no warranty or guarantee of soundness or suitability to purpose."
In other words, if I show you a fully trained western pleasure horse and 3 months from now you come back and say, "This horse won't jump", too bad, I never said the horse was a jumper. Get it all in writing and both you and the seller sign and have someone witness if you can.