Okay, you've done your homework, selected a great breeder who titles and health tests their dogs, selected a great match for their dog who will produce a generation of puppies that improve the breed. The last piece of the puzzle is to assess how they raise their puppies.
Within the breeding community, there are two structured programs that have been refined and demonstrated to produce well-socialized, confident, and resilient puppies: Puppy Culture and Avidog.
Puppy Culture provides a week-by-week guide on things to do with your puppies to gently challenge them and increase their exposure to a variety of textures, surfaces, sounds, and scents.
The Puppy Culture is a 12-week program that requires a sizeable investment in time by a breeder, but the results have shown that puppies raised via Puppy Culture are more confident and resilient to stress. To a breeder who cares about the long-term well-being of their puppies, this investment is well worth it to set their puppies up for success. There is also a program to guide new puppy owners as well, if they choose to continue to work on socializing their puppies.
When researching breeders, you can ask whether the breeder in question follows any specific protocols or programs to help ensure their puppies are well-socialized. It's also quite easy for a breeder to claim they do something - check out their social media to see if there is evidence that they're actually performing the exercises, such as Early Neurological Stimulation (ENS) where puppies are exposed to various textures and temperatures in a controlled environment to safely stress them.