Well, I can see both sides. Frankly, I would be a little annoyed with the bridle question. You are a novice owner who has just purchased a high priced horse. I certainly would hope that you did not do this without consulting your trainer, and I would hope the trainer went with you to see the horse and perhaps ride it. I would agree that your trainer should be able to guide you as to bits, etc, and that is the appropriate place to start. First, you are paying them to help you. Second, they know how you ride, so would be more apt to use appropriate bit, etc.
I also agree with the people who say you most likely bought this horse through a broker/agent. They buy and sell many horses, and that is a different situation than from an individual. However, given the fact that you still owe them a substantial amount of $$, I find it a bit strange that they are not making nice!
Over the years it has been a mixed bag for me-Some I stay in contact with, others not, and one-well that was the only one I could not have cared less about.
The good news is that if there are going to be "surprises" with your purchase, you still owe them $$, so you may have some recourse, but only if it is something blatant (like drugging, etc) since you had the horse vetted and recieved a reduction based on the results.
Remember, all horses have some idiosycracies, just like people. The key is to figure out what it is for that horse and then decide if it is something you can deal/live with.
Good luck and have fun with your new horse!