As a riding instructor, trainer, and riding student, my advice is to go to the facility that you are looking into, unannounced. If they tell you that you have to set up an appointment to be there, I would be skeptical about leaving my horse there. Showing up unannounced, you will be able to see the true way these people work. If they are trying to hide something, they will be more able to do so with an appointment. Also, go and watch them ride or train. And ALWAYS ask questions. If they can't give you an answer or they beat around the bush about it, they may not know what they are doing. Only you can be the judge about what is the "right" trainer for your horse.
Hope this helped(:
Soft hands. Strong Legs. Steady Mind.