I understand where you are coming from! I had this same dilema two years ago when I decided not to train my own miniature for fear of wrecking myself and the horse. I went to a clinic put on by an area miniature horse club that featured a trainer giving demonstrations. After watching what he was doing and how he treated the horses and talking with the other people at the clinic that had done business with him in the past I decided that this was the trainer for me and I have never regretted it. My advise would be to ask around and get recommendations. Talk to current clients and found out how long they have been with the trainer, check out their website, if they have one, to see what they have done in and out of the ring. The cost was the scariest part of it but I decided it was worth the money. I have a rock solid horse that I can drive anywhere and so can anyone else. Which brings me to the other part. It is one thing to have the horse trained but another to have the person trained to drive the horse. My horse was trained in a little over two and a half months but I was not. I drove 3 1/2 hours one way to have a one hour driving lesson nearly every weekend for six months so that I had the confidence to be able to handle any situation my horse and I were put into including other horse traffic, noisy trucks, firecrackers, all types of odd noises that could potentially spook a horse. All of this was accomplished without a contract. We spoke about the fees which are posted on his website and I obviously saw my horse frequently for my lessons but I was also encouraged to call or stop by anytime. My trainer has insurance on my horse and all the others he trains. Good things aren't cheap and cheap things aren't good. Do what feels comfortable and if it doesn't feel right - don't do it.
Good Luck!
