I have given away horses to friends I trust and sold a couple, I guess they went like this (not all in this order):

Halter trained long yearling who was an untouched rescue, went to a great home where he was started. They purchased as a partnership, one sold out to the other who furthered his saddle training and sold him to a young rifer. He was later for sale as a low level dressage horse for 10x the original purchase price and found a great home where he is showing in western classes. So he has been through 4 homes and all of them good. Myself or his second owner would be fine with helping or taking him back if needed but he probably will not need it. Current owner has invited us both to visit any time.

Pretty well trained 11y/o saddle horse that doesn't really fit our needs sells to retired couple who take him camping and trail riding. He seems happy and we get regular updates. They have someone pet sit and he is injured but still functional for their needs. At a later date he accidentally stomps a pet sitter's chihuahua and the owners give the horse to the gal in lieu of paying vet bills on the dog. I get a call about this not from the people I sold to, but from the new owner who has no use for the horse but is honoring my buyback clause. I'm not in an immediate position to take him back but I help network and arrange for some folks to go try him. They say he is nice but not sound enough for their needs. Someone else comes promising the horse a great home doing mostly leadline with kids. Horse is spotted again as a freebie and there is no reply on his whereabouts for the last point of contact. I hope he found a great home, and I wish I had been in a position to take him back.

Older gelding labeled dangerous to haul comes to me with a contract indicating he be euthed if his behavioral issues cannot be managed. We share ownership with friends who never needed to haul him, where he was a loved family saddle horse until his death.

We rescue an old neglected dude stable horse and again share ownership with same friends where we help rehab, he gets healthy and is a beloved child's horse. He lives longer than expected and stays with that family until the end.

Young horse given to a good friend became a great saddle horse that I visit and ride and will take back no question if there is ever a problem.

Old retired arthritic mule comes to us as a package with another retired mule, he goes to a friend who manages his needs and keeps him as a happy pet until the end.

Old retired mule came to us when her 40 y/o companion died is shared with a friend where she taught kids to ride, lives with us a couple of years until the weather is too rough then goes back to trusted friend until the end.

Young horse who was given to us, rehomed to a student of a friend. She had good care and became a great saddle horse for the family and I still get updates occasionally. She is probably with them for life but they know she could come back if there was a crisis. A couple years later they end up helping us find our ranch and acting as our agent.

Pretty difficult horse from another rescue we took on to get him well started and gave to a friend, he didn't work out as a saddle horse but is a very well cared for pet and mascot for her ranch and the poster child for an annual horse fair. We said he could come back but he will be there for life. We visit him sometimes but get updates regardless.

Green saddle horse traded to a friend for her dangerous unbroke horse, saddle horse is a cherished member of the family (we get updated) and unbroke dangerous horse was trained and rehomed where he is loved and useful and there is a buyback clause.

Nicely started rescue pony that I trained was sold to nice family, spoiled and sour comes back for re-training and needs advanced rider. Subsequently is given to me where we do more training then he rescue friend and finds a home working cattle where he is useful and happy with a buyback clause.

Young horse rescued by a friend, we started and gave back to her is a family horse and works as an all around great lesson and trail horse for children. Of course he could come back if needed.

Young pony we rescued but couldn't keep safely with our own horses was placed into a rescue where we had faith she would find a home. The rescue had an unrelated strangles outbreak and neglected all horses maintenence for 8 months, we find pony in with a stud colt and immediately take her back, trim, tune up. We are not in a great position to keep her but find an add seeking a companion and meet Gasmenagerie where she has an awesome home for a couple of years. Then she came back to us when the need arose and is here.

Colt loaned out for free as a companion. There is an option to make it a permanent home at a later date. A few weeks later I hear fro a 3rd party that "it was sad that so and so sold the horse you gave her." Discover that so and so used a false name (so the references would check out) and is a known scammer. Scramble and sort through all kinds of stories to the horse's actual location then calls to law enforcement to advise. Follow advice from law enforcement and things don't go well because law enforcement didn't advise the proper chain of events. I should have gotten a court order and because, albeit illegal, a sale was involved. I would have had to reimburse the (non-citizen) buyer who wasn't aware that the horse was stolen. Meanwhile my horse disappeared overnight, and nasty scammer assured me that my horse went to MX and it is entirely my fault.

Now I'm gun shy

We still had our 11 or so horses the whole time these others passed through. Currently have 16 and none seem to be leaving in a hurry without going to a very well screened and suitable home or long term lease. Of course they will have a first right of refusal, and probably a trial period too, they are not just commodities.

"It's really quite amazing what a horse will do for you, if he only understands what you want. 
And it it's also quite amazing what a horse will do to you if he doesn't." ~ Bill Dorrance