Both owner and trainer can benefit. Some owners want to deals only with the "hot chem" trainers. They will leave them in a heartbeat and if things go south leave them broke. Some trainers
are desperate to get horses and take a bad deal for themselves or get only broken down horses who can't do. But if you have a good relationship and are looking out for each other interests, plus classify as needed both can do well.
1) never buy a horse the trainer doesn't want
2) if the horse cannot do, move it so the trainer doesn't get killed. That does not mean panic but after two to three months if the horse cannot do you have to take your loss and move on.