Yes, I think if you want to limit a horse’s jumping height, that should definitely be in the ad. I don’t think it’s unreasonable for people to lay out what they were hoping to do with a horse when you haven’t put any specifics in your ad as to what the horse is capable of or what your limits are.
If you put in the ad “horse cannot be jumped over 2’6” at least some (but not all) of the yahoos will move on and you will get people who are more the type you are looking for.
I don’t think a shareboard price necessarily reflects what a horse is capable of, either. I know the rule of thumb is that a full lease price is a percentage of the value of the horse, but shareboarding really doesn’t follow that vein. I know some very nice and talented horses that were offered for partboard (the Canadian terminology, lol) whose partboard price was very reasonable because the owner just wanted a second rider for the horse, because they couldn’t get out enough.
So be extremely specific about your limitations and requirements in your ad. I would also suggest that once you find someone, you drop by unannounced on one of “their” days with your horse just to make sure that your wishes are being followed. The number of people I know (or that I have personally caught) doing more, a LOT more, with a leased or partboarded horse, is huge. Even if your trainer is involved, if this person is going to be allowed to ride your horse unsupervised, you have to be diligent to make sure your horse is being ridden how you have directed. (I once caught a girl who was partboarding and not supposed to be jumping outside of lessons at all, jumping full courses with the horse. She was pretty new to riding and didn’t see any issue with jumping oxers backwards, etc because she just didn’t know. It was obvious WHY this girl should only be jumping under supervision, but she didn’t care. And yes, I reported back to the owner what was going on.)