This will tell you a lot about the breeder. Puppies are very impressionable until about four months of age. They learn from adult dogs. If they are around friendly dogs, they learn to be friendly. If they are around aggressive dogs, they learn to be aggressive.
Some mother s are very protective of their litter when strangers are around.
Do not be afraid to ask questions. If the breeder seems offended that you are asking so many questions, or gives you the run around, then maybe he has something to hide. Ask all kinds of questions to find out how knowledgeable they are about their breed and dogs in general. Since you have researched the breed you are looking at, you know the basics about the breed. The breeder should know the main health concerns of the breed off the top of their head.