The reputable breeder of Champion show dogs has invested a great deal of time, money and energy into producing puppies that he or she has worked to ensure will be healthy examples of the breed.  They can't keep every puppy they cause to be born, so some are available as pets to people like you. The differences between the puppy from a reputable breeder and back yard breeder (BYB) puppy (such as you find on Craigslist or in some Facebook groups) are:
Reputably bred puppies come from parents who have been health tested - minimum OFA, patella, CERF.  BYB puppies rarely are.
Reputable breeders are conscientious about breeding good genetic lines. They have researched pedigrees to reduce the risk of genetic illnesses like hip displaysia, entropion, or temperament issues like rage syndrome. BYB breeders don't care - they just want to sell puppies.
Reputable breeders show their dogs in AKC events to various levels of Championship - which means the dogs have been judged worthy of breeding by a minimum of three qualified AKC judges. BYB breeders do not show their dogs, so they do not compete against other dogs by any ethical outside entity to determine their worthiness to reproduce.
Reputable breeders are members of clubs like ACA, and agree to adhere to ethical breeding practices. Back yard breeders do not.
Reputable breeders will mentor, stay in contact and follow up with puppy buyers for the lifetime of the dog. Back yard breeders do not.
Reputable breeders will offer and honor health guarantees on the puppies they place. Back yard breeders do not.
If you can't keep the dog for any reason at any time during its lifetime, the Reputable Breeder will take the dog back. The BYB will not.
Reputably bred dogs do not end up in rescue. BYB dogs do.
Back yard breeders are only after the money, are not interested in the health of either the parents or the puppies.