I had one with a strained superspinous ligament - detected by scintography at RVC. The treatment was a single steriod jab to make her comfortable tenough to do rehab then physio / rehab exercises to build up strength.
Introducing an older horse he knows / likes may help. We put our then 6 month old and his his dam in with our 2 and 3yo geldings (who had been together for over a year) along with another retired mare. The mares kept order and, as he got more confident, the smallest one spent more time with...
How long has he been with them? It can take a while for a new younger bone to be integrated. Our older mares were horrid toour new 3yo for a few weeks. Wouldn't let her graze with them. She was eventually welcomed into the mini herd.
When I was looking I found expanding the age range and height range, ignoring colour and being flexible on breeding helped me get what I wanted.
I’d maybe focus your advert on what you want to be able to do with your new horse and a short list of genuine non negotiables.
I think we do over analyse. There are so many sources of information (much of which is questionable), a myriad of different feeds / supplements and far more diagnostic / treatment options than there were before. And it is increasingly difficult to find places to keep horses whee they can get...
I wouldn't want a yard to do anything other than handle my horses quietly and calmly and certainly wouldn't tolerate a yard owner attempting to 'put manners on them'. However they are generally easy horses to deal with and I would expect to be notified of any change in behaviour.
I don’t think it’s as simple as under or over horsed. You need to factor in how the horse is to be kept (compared to their current setup), how fit you are going to get them and whether you are the sort of rider that makes horses more whizzy or sends them to sleep.
Won't compromise on nice person, young, big, well bred and mare. Will compromise on talent, experience and conformation. Might compromise on soundness (if reason known).
I would get workup from a really good lameness vet to pinpoint the cause, with whatever Xrays they think are needed plus foot balance X-rays.
Once the underlying cause is addressed, I would have an intensive course of indiba and get a really good hoofcare professional to address any foot...