There are many cases where that proven, expensive horse turns out to be the better bargain. Another question to be considered involves temperament. If the mare is mean and hard to handle, or nervous and flighty, there is a good chance that her foal will be the same. Not only does the mare have the potential to pass on these qualities genetically, she might reinforce them with her own behavior. The foal is tightly bonded to its dam during the first weeks and even months of its life, and often mimics the mare's behavior patterns.
Conformation also is important.
If not, be careful, even if the mare has remained sound. The problem could be compounded in the foal, especially if the stallion has a similar problem. Here again, your veterinarian is your best ally. Have the vet give the mare a thorough examination, especially if she is older. There might be serious uterine scarring or the presence of cysts that could compromise her ability to carry a foal to term.