Hi KV, yes I do let certain people ride my mare T. Only with me and usually at a walk, possibly a trot here and there . I am very selective who rides her, for her sake as well as mine. Yes if they get hurt the potential to be sued is there, even if they sign a release.
The rest of the people that hear I have horses and drop very heavy hints about riding them, I tell them that I am not insured for riders. I do not own a riding stable or school, so that takes care of that.
It is annoying though, that people think riding a horse is like riding an ATV, but I have the choice to say yes or no. Don't ever let someone pressure into allowing something you truly are not comfortable with.
As far as knowing whether the horse will behave for the rider.....well you truly don't. No matter how well behaved that horse is for you, that is not a guarantee it will be for an other rider. T, wonderful as she is with me, acutally reared (not very high, but still a rear) with a girl that had been riding her with me during the summer. No matter how well trained or schooled a horse is, things can happen. Part of the risk of riding. I know why she reared, at least I'm pretty sure, it was resistance to taking a certain trail. Has resisted at that point with me in the saddle , but all I do is put my leg on her just prior to the balk, and sometimes sternly say "T, cut it out" and it's over. Put a different rider and same situation takes a different course.