I agree with you that you should never buy a pure breed puppy from a puppy mill or backyard breeders. Puppy Mill kennels dogs live his or her entire life in a small wire cage with no human companionship, which essentially means they are not rasied in a very social and clean environment where they are loved and played with daily. Never buy from a pet stores! Pet store dogs might say they're purebred, but its not a good thing because they were most likely incredibly inbred at a puppy mill.
Animal shelters may be appropriate sources of pets for families with low budgets or the desire to save an unfortunate dog from euthanasia at a kill shelter but, adopting a dogs from a shelters does come with some of its own inherited problems. Shelter shoppers should beware that many dogs are impounded or surrendered because their previous owners failed to prevent or solve behavior problems. The vast majority of dogs in shelters are mixed breeds, so even if the dog is full grown, judging its temperament, breed-related behavior, and trainability is difficult for inexperienced pet owners to determine. Plus, although shelters are doing a good thing by spaying or neutering your puppy, they sometimes do this too early, and the puppy can get future complications. However, a patient and discriminating person can find a dog that appeals to his own personality and needs at a public or private shelter for a very reasonable price. IMO the major reason many people choose to buy prue breed puppies over shelter dogs is they feel they will be able instill proper obeisance training at a very early age.
With a mutt, you have no idea what kind of diseases it could have just in its DNA. IMO purebred dogs can be better than mutts because the lineage is known. When you buy a purebred puppy from a reputable Private breeders it can be a very positive experience, because a reputable Private breeders knows there bloodline lineage and have breed out health problems like joint disease, blindness, eye problems, etc . Picking a responsible AKC registered breeder is just as important, as choosing the best breed that will fit into your family. The Breeder should be able to answer any questions about the puppy they are selling and allways provide a health guarantee, Veterinary check, initial vaccinations, dewormed and health records on all the puppies that they sell. The breeder should always show you aleast one of the two sire or dam onsight. If the breeder does not offer these things. I would look elsewhere!!!