backyard breeders breed puppies and have "accidental" litters. When there is nobody else willing to pay for their puppies they are advertised as "free to a good home". In fact, there are lots of people that don't breed who give their pets away "free to a good home" and don't even realize that people are taking them to breed and sell the pups to pet stores as some outrageously priced designer breed or even as "purebred". This is what happens to those puppies that don't find a good home or end up euthanized in a shelter. Why is it less than 30% of all dogs bred make it into a good home?
Backyard Breeding - YouTube