Even at this young age puppies have very distinct personalities. Some breeders temperament test their puppies, others rely on hours of observation and experience as the puppies grow up. Some puppies require more experienced homes either to contain an opinionated personality or bring out the best in a shy one. No puppy should go to its new home before 8 weeks of age except in extraordinary circumstances. They need this time with their brothers and sisters in order to learn to be dogs, and also such important things as bite inhibition which will make them much nicer companions.
Health is also very important.
While these two conditions are uncommon in the breed it is a good idea to test for them so that they do not become more common in future generations. The breeder should be happy to show you the results of the tests if you ask her. Because you are buying a pure bred dog he should be a recognizable representative of his breed. You do not want to buy a dog with a serious problem however, or one with a bad temperament - hyperactive, extremely fearful or aggressive. The breeder should be happy to discuss all your questions with you, and she should be there for you and the puppy for the rest of his life.