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There can still be some uncertainty from a given breeder. Our last Berner (Bernese Mtn Dog) came from a breeder in Maine, after we had visited an d rejected litters from other breeders. 10 pups, all true to the breed. The breeder had tried a new (young) stud, and just for safety had bred with an old reliable. DNA testing revealed that all 10 pups were from the old guy and the kid had not performed his duties successfully.
You can check breeders and lineage on AKC.org, and most breeds have their own website as well.
Milo Pearsall "Dog Obedience Training" has excellent info on how to evaluate puppies within a litter, available, used, on Amazon or perhaps through NH inter-library exchange.