CHT...you are right in possibly letting someone ride an older/bombproof horse to get them back into riding. I have done that a couple of times, but was right with them.
As for my "good horses", I can count on the fingers of one hand how many people have ever ridden my Palomino, since I've had him, and have 3 fingers left over. And that is in 12 years.
Baby Huey I have put someone up on, in round pen only, and did let my daughter ride him outside it, where he went to crow hopping and she bailed, (never taught her what to do, since only had ridden her horse who didn't do things like that) and other friend rode him too.
But by and large, I won't let people ride my horses.
I'm really picky about hands, so makes me nervous.
Horses make me a better person.