I agree with you all BUT I think I was misunderstand re: "trying" the rider. I have bought/sold several horses that were retreads either bc they were spoiled and misbehaved then sold, or, frightened and acted out, then sold. These horses had some potential in the eyes of low level trainers, really cow punchers who have "turned them around". They ride for the trainers but are looking for a way out from anyone who doesn't either install confidence and/or establish leadership. If the next buyer does neither, in my experience, the horse bucks, rears, plants feet and explodes, etc. in an effort to NOT repeat the original bad training experience. We do the same if we've been beat up in the workplace, so it's understandable.
After I was thrown in 2004, I lost confidence and I bought a few horses that I might have turned around when I had my lesson program bc everyone had to work or be sold, AND, I was much more athletic in my 30's than in my 50's. Each was okay for awhile, then started to refuse work.
I think that THIS mare is as Cherie has described.
I think if you buy a horse that demonstrates these behaviors, you NEED a trainer or a training method. I don't think that she is vicious and horses don't have agendas. Horses just want their work to be pleasant and when trained correctly they enjoy the endorphins just like humans athletes.