A reputable breeder will have a vast store of information and support going into whelping. It is important to look at where the puppies are kept while still with the breeder and how they are raised. For instance, a good breeder will have a proper whelping setup that is easy to clean and sanitize, as well as cleaned out rather frequently.
In addition, a good breeder will put a lot of effort into socializing the puppies. Some will follow various programs that help work through early neurological stimulation, enrichment, fear and development periods, crate and potty training, anti-aggression protocols, problem prevention, and much more.
In addition, a reputable breeder would not allow a puppy to leave their home until they are a minimum of eight weeks of age. Puppies need to learn and socialize with their mother and littermates at least until 8 weeks of age. Some breeders will keep the pups until they are 10 or 12 weeks old.