It would greatly depend on the details. How long would the training contract be for? What type of stipulations would be in the sale contract for if the horse was injured or otherwise unable to continue training (for example a stallion who had an eye injury making him unable to show, but not affecting his career as a breeding stallion)?
It is a good idea. I just looked at your training rates on your website, and if you were in my area, this is defiantly something I would look into. If it were a trainer with high rates and was a long contract, I probably wouldnt. I wouldnt want to be paying more than the horses value in training if the whole Idea was the horse was free. Hope that makes sense. Personally, when I do use a trainer, I like my horses to be within 4 hours of home, simply because I also show ammy, so I take lessons from the trainer while my horse is in training. Much further away, and that's not feasible.