Before There Were Bad Owners...There Were Bad Breeders...
Many breeders are respectable and reputable. But many are out to make a fast buck and don't care about the health or the temperament of the animal. Sadly some people breed dogs for the sole purpose of dog fights.
When choosing a breeder and buying a pet you need to be alert and trust your instincts, you should be able to see where the dogs are kept, meet the mother (and possibly the father), ask from references from previous customers. If it doesn't feel right trust your instincts and look elsewhere.