I often look at other breeders website's as I am constantly looking for new stud dogs to bring diversity to my lines, so I want to see their dogs and their dogs registered names. This tells me that their dogs are registered with a governing body like the Canadian Kennel Club (CKC) American Kennel Club (AKC) or Eurpeon Kennel Clubs etc. and that enables me to look up the pedigree information to see if this stud dog would suit my female. I also look to see if their dogs have all health testing done, like hips and elbows via OFA, BVA, FCI, OVC, heart by cardiologist, eyes by opthamologist and the appropriate DNA testing.
I check out to see where their puppies are raised. Are they being raised in a barn or a house, I look at the background in some pictures. Are you seeing just a cute puppy picture with the puppy being posed. When I don't see a clean play room in a house with lots of toys, dogs, TV etc. I wonder how they are being socialized and cared for. I look for consistency in the background, is the puppy always outside? Is the furniture or flooring the same in different in photos? It is very easy to steal photos off the internet.
How much experience do they have? Have they been breeding for years or are just starting out. Look to see past and present dogs. Is this the type of Golden Retriever you are looking for? There are different types/styles - British/English lines, American lines, Working lines.
Are they members of the Canadian Kennel Club (CKC), Golden Retriever Club of Canada or a breed Club in their vicinity.
Be prepared to wait, most good breeders have a wait list.
Hope this helps narrow down your search.