"If a saddles does not fit the horse or rider the saddle must be returned unused. Please note that saddle returns are subject to our 10% restocking and handling fee. When fitting a saddle for your horse use a clean blanket or towel before placing on your horse’s back. We do not accept returns on used saddles."
I'd be REAL apprehensive about buying a saddle online w/ that kind of return policy, especially since it sounds like your horse has a history of being hard to fit.
ETA, I stopped by to look @ the saddle description. Sounds like it's built over a rigid tree, and claims to be "full quarter horse bars", but at least one reviewer says it is VERY narrow.
Way back in the day, I used to shop from Stateline Tack via their catalog (before online shopping was a thing), and something I realized really quickly is that almost anything leather from Stateline wasn't typically very good quality.