Bear with me. This is a bit off subject, but getting into minis doesn't necessarily have to mean breeding minis
Many people start out with driving geldings or non breeding mares to train, show, play with, and love. The sky is the limit for what you can do with minis. Therapy horses (nursing homes/therapeutic riding), 4-h, halter, obstacle, driving, walking buddy, giving kids horseback rides, a pet to love, etc. Even if you have a lot of previous experience in horses I think there's something to be said for starting out slowly before you know if breeding is what you really want. I know the desire to breed horses can be great, I certainly had it and still have it, but I thank God that I had a gelding first and waited several years to break into breeding. That way I knew for sure and put my whole being into the process. Still consider myself a breeder, but no mare is bred for next year, and perhaps none will be bred for 2013 either. I do not intend this as a lecture or condescension, this is just my opinion as a reflection of where we are as a breed.
That said, we all have different opinions one what is a good deal. Have you asked about the mares foaling history? Or if she ever delivered a foal with dwarfism? Is she a maiden? How old is this mare? Does she have difficulty getting in foal? Have you seen pictures of her previous offspring? A deal can be a deal or it can be just too good to be true. I have had the pleasure of dealing with
very honest sellers in this breed. Every seller of minis in the past 13 years of mini ownership has been wonderful. There will be some sellers (of anything) that feel that they must not tell the truth, or at least not the whole truth in order to get ahead. You learn quickly that a good seller will tolerate all sorts of probing questions, whereas a bad one may take real offense at these questions. As a seller it is better to be honest to a fault, even if it means a lost sale, imo. As a buyer, the more questions you ask a seller the more they should realize that you really care.
As an addendum, I have seen more dishonest dealing in large horses. Lies about horses cribbing, lies about previous colic, lies about the amount of training the horse has received. There are many more honest miniature horse people in my experience.