I don't think I know any Horse Trader - who isn't a liar. The saying around here goes "Buyer Beware"
You may have had a bad experience or know the wrong people, MOST of the horse traders, the genuine horse traders I have known have been great to deal with. Because their business is to buy and sell they need repeat business and word of mouth in the horse community can kill you stone dead.
So while BUYER BEWARE is teh watch word anytime you go to buy a horse, a good horse trader can be a great place to visit, they tend to have a range of types of horses, and the guy I worked with a lot found me 2 gems when I was looking.
I couldn't imagine buying a horse sight unseen. I think that's asking for trouble, but there are plenty of liars and people who want to make a quick buck that anybody can be done over with them.
It's done more than you think, I have both bought and sold sight unseen, this is a kind of Haflinger desert up here, and it would cost me more than the cost of the horse to go and see them, so I have bought a few from videos, pics and conversations, hey, even Big Ben here was bought sight unseen. I have only been lied to once, and that was from a breeder, who seems to be respected in her breed, she downright robbed me, but the small town breeder, the trader and the private person I've dealt with, full honesty and full disclosure, I knew what I was getting and was happy with the deal.
OP, suing anyone over a horse deal is hard, I did manage to get a little money back from my one sour deal, but it still left a bad taste in my mouth. If the horse you bought it sound and healthy, just not a good match, sell it and move on, or take it to a local reputable dealer and trade it in.