Oh Lyn.........You are in that horrible "gray area" in regard to buying and selling a horse because there was NO CONTRACT.
Legally, the money was exchanged for a horse with permanent registration papers, as promised and I assume there was a sales receipt and transfer forms signed. So legally, the buyer is now the owner of the horse. And legally, that would be it and if the new owner wanted to, they could sell the horse anywhere and for any amount -- tomorrow!
HOWEVER, we all know that horses who are "close" to that magic 34 number can flip-flop on either side depending on who is measuring, the weather, hoof length, how the horse is set up, or even if the sky is blue and not gray!!!!
The above measurement issue WITHOUT a contract opens up a can of worms to an HONEST SELLER. Yes, we hear more about Buyers getting burned, but Sellers can too.......if they are honest and want to be respected.
The other issue not mentioned (yet) is......As the seller, do you want this sort of person to have ownership to YOUR horse?
It sounds as though, for whatever reason, the Buyer is trying to get out of the deal........and the measurement issue is a handy one. "Legally", you don't have to take the horse back, from what you described. BUT.......the concern over how will your horse be treated or where will it end up may also be a consideration.
Just a thought to make it more difficult for you............Sorry.......
PS: I just noticed you were also asking about the transport? That's also a sticky wicket. The FAIR thing would be for you two to split the cost. But it doesn't sound as though you are dealing with a fair buyer either.........