It is a big problem we are talking about here and I think it is only one approach to solve it by not buying from a pet store. IMO if we are really serious about shutting down puppy mills we have to take other actions too
1. put pressure on the kennel clubs to not give out registration papers for puppies from puppy mill owners
2. put pressure on the legislative for a effective law against puppy mills
3. and another law to forbid selling dogs and cats in pet stores at all (like there is in other countries)