Well, what I am saying is, equine rescues may have connections which may help the man trust who his horses go to.
All rescue organizations have procedures that they go through for potential adopters, policies which the potential adopter must follow, have references and whatnot.
Perhaps you can convince him to work with an equine rescue organization to help him get his horses placed. Rescue orgs have websites which they potentially could post his horses on, have connections with people who could or would be willing to take his horses in, and they would be bound to uphold the stipulations written in the adoption contract. I am sure a rescue would be willing to help, especially if the horses will be staying at his farm until adopted out.
He might have to donate a portion or all of the fee he could potentially get to the rescue though, which he may not wish to.
Or perhaps he could send his horses out with a rescue organization type contract. If you look at several equine rescue org. websites, you can get examples of the adoption contract.