Reputable breeders have a deep interest in where their puppies go and will interview hopeful buyers before a sale is completed. Reputable breeders will not sell their dogs in any way that does not permit them to have interaction with potential buyers. Their desire is to ensure that the puppies are a good match for the families and that the puppies will go to a responsible, loving, forever home.

In contrast, puppy mills are commercial enterprises which breed dogs in significant numbers for profit. While puppy mills are not inherently illegal, their operators use the dogs as nothing more than income producing machines. Maximization of profit allows for no screening of genetic problems and veterinary care is minimal, if provided at all. Any provision for the comfort and well-being of the dogs shows up as an expense in the accounting ledger and must be kept to an absolute minimum. Dogs not on display for potential buyers are kept in cramped wire cages twenty-four hours a day, often left unprotected from the winter cold and the summer heat.

In many instances cages are stacked one on top of another, exposing dogs in the lower levels to the excrement of those above. Females are often kept in a state of perpetual pregnancy until they are no longer able to bear young, with no hope of ever becoming part of a family themselves. Dogs that have outlived their usefulness for breeding represent nothing but a nonproductive expense as far as the operators are concerned and are usually killed.

Most pet stores purchase their puppies from puppy mills. Such stores want "product" in volume for the lowest price possible and that's what puppy mills are in business to provide. Pet stores sometimes rely on the relationship between families and their new puppies being so strong that puppies who begin to exhibit health or behavioral problems will not be returned. Wanting to "rescue" a puppy from its cage at the pet store only reinforces the cycle of supply and demand that keeps puppy mills profitable.