Ask for names of owners they sold a dog to that may live near you. Remember you are buying this dog almost sight unseen. Be very specific about what you want in terms of color, size, temperament and quality of the dog . Also you want an agreement that you have at least 5 days to take the puppy to a vet for examination, and the puppy is returnable if their is a health problem uncovered by your vet. If you are a new owner of a dog, be aware that there are specific genetic problems in many breeds of dogs.
Large dogs are more susceptible to hip problems called Dysplasia, than small dog breeds.
The AKC and many breed clubs have official records of tests for these congenital problems. They are called OFA for radiological hip examination, CERF for eye problems that lead to blindness. If you are a new buyer before you buy this breed make sure the dog is suited to your family and your home environment. For example as a Lhasa Apso breeder we almost never sell a Lhasa puppy to a family with very young children. Why, because a Lhasa is a very intelligent aggressive guard dog.