The only way to end puppy mills is having no customers.
Puppy mills continue because there are people who will buy these frequently sick, many times genetically affected by inbreeding, pups.
If people only buy puppies from reputable breeders, breeders you can GO to the house and see the conditions, the puppy mills would have to shut down because they couldn't sell them.
Also, inquire about the origins of a puppy you buy at a pet store.
BEST BET: ADOPT! There are so MANY good boys and girls that are desperate for a home.