Here is the judgment of Solomon, given that as we know any sale is a betrayal of a long term family member however redundant and annoying they may objectively be. Indeed many Funded would contemplate extreme measures rather than risking an horrendous chain of onward sale in a downward spiral to the knackers yard. And you cannot blame them – in this even a hard hearted Funder must have some sympathy.
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thehorsefunder 
No more information than that? It’s hard to sell a good horse. It’s nothing off your heart to sell a bad one. I had a horse..a bad one, who very plainly hated humans, who tried to hurt anyone who rode him, who was not a very nice horse. After several buyers came through and looked at him, one man clicked with the horse and we sold him to the man. I saw the man about a year later on the horse, and he was going so nicely I began to question my judgement. But that’s horses can be… For him, the horse worked well.
So I would say: and I know how hard it is, emotionally, but you sell the horse that no longer can do the work you want of him, the horse that is unrideable, the horse that has so many medical issues that your vet has you on speed dial, the horse that is picked on, bullied and otherwise used as a kicking post by the other horses.
You can’t avoid the guilt. You will never get over the guilt, but sometimes, you have to sell one.