what should you get in writing from the previous owner (in this case, a dealer)? Have heard of so many people having bad experiences I don't want to get caught out!!
You can only write what they have said to you. No horse is perfect, so remember they will tell you all the good things. Ask lots of questions and then you know the answer. Might be best for a trial if they will let you. A horse is not like buying a car, its a living thing and can behave differently with someone else...