In my opinion, anyone who puts their dog in a pet shop is a puppy mill. A "mill" is something that supplies. If you breed your dogs for the purpose of "supplying" a pet shop, you are a puppy mill. But then there are accidental litters -- not bred for the exact purpose of supplying a pet shop. Most people think of puppy mills as big dirty disgusting places with cages heaped on top of one another --- as far as those go, statistcs say that 9 out of 10 puppies in a pet shop come from one of those.