The vast majority of puppy mill animals are sold to pet stores by dealers.

Sometimes the puppy mill owners will have a contact person who collaborates with rescues.

Their popularity has led to 'merciless back-street breeders and puppy mills'.

Recognizing the high demand for purebred animals, some people choose to engage in backyard breeding or operate puppy mills.

Kitten mills are not as widely known as puppy mills, but they still do exist.