What If Pet Stores Only Sold Rescue Animals?

What if all the pet stores in Billings could only sell rescue animals?  Do you think that is a good idea?  Would it slow down the puppy mills?

San Francisco pet stores are now only allowed to sell rescue pets. The amendment will also prohibit the sale of puppies or kittens under eight weeks old. According to SFgate.com My last four dogs have all come from the shelter or Conan my Mal, came from a breed specific rescue.

As someone who supports shelters and rescues I love this idea?  Do you think this would be doable here in Billings?  Would it help the pet population?