When I was outfitting we had a written disclaimer that was required to be read and signed by each hunter before they could do anything. It started like this, "Horseback riding is an inherently dangerous activity" and on to basically say that the Outfitter could not be held liable for any damages. I would have never even considered putting a client on an unknown animal. Our "Dude stock" was so dead broke that they would never even consider bucking. They knew that took extra energy and they needed all they could get for what lay ahead!
Saddle mules are the real way to go. I want one this next year hopefully. I have two great old geldings that are 20 now, and would like to switch them over to strictly just packing or a dude friend now and then maybe.