Puppy mills: Only reason to exist is to make money.
Hobby breeder: Emphasis is on breeding for certain qualities (depends upon the venue). Rarely make a profit.
Puppy mills: Generally have at least several breeds, often more than 5 different breeds.
Hobby breeder: Most of the time focuses on 1 or 2 breeds.
Puppy mills: Generally have puppies available all the time and usually sell puppies via some other outlet (pet shops or brokers)
Hobby breeder: Generally breed only a few litters per year and sell their puppies themselves (and carefully screen buyers).
Puppy mills: Are not there for the buyer after the sale.
Hobby breeders: Are there for the buyer for the life of the dog.
Puppy mills: Usually do not do any genetic testing, usually breed females at each season until they cannot produce enough puppies.
Hobby breeders: Usually breed a bitch no more often than once every year and frequently not that often, usually only have a few litters from one female, and then they are spayed and retired by age 8.
Puppy mills: Do not do anything other than breed their dogs.
Hobby breeder: Competes or tests their dogs in some venue.
There are certainly things I have not thought of, but there's a start for you.
susie
I'm on your side of this argument, but any law is going to have to quantify in order to define what is being regulated.
I live in Pennsylvania and have lived in Lancaster County (where the Amish crank out puppies like any other livestock). Successive dog laws have failed to put much of a dent into volume breeding business there. OTOH, zoning laws limiting households to 2 dogs have really put private breeders in jeopardy. Get that 3rd dog and your local township considers you 'a kennel'. In this case, the number is unrealistically low.