There is really not much more I can add to what has already been said, but I have to put in my two cent...
NO serious breeder would EVER put a single of their puppies in a petstore!
1. There is no way of knowing who will get the pup since there is no screening process. There is a reason breeders (and rescues!) so thoroughly screed potential owners, not everyone should own a doh and not everyone realizes that they're nor ready to own a dog. There are 6 million dogs euthanized every year due to pet overpopulation and mill/pet store dogs are a HUGE contributor! So many pet store puppies end up in shelters because people didn't realize how much work goes into caring for a dog. I'm a rescue volunteer, and just talk to me the first week of january when we are swamped with Christmas puppies!
2. The crucial first months of a puppy's life when he/she should be interacting with the mother and litter mates, getting socialized, etc. A pet store puppy spends in a cage, often resulting in social and behavioral problems, no breeder would do that to their dogs! You don't whant to know what happens to the poor dogs that don't get sold and loose thir cute "puppyness". Believe me, they don't get "adopted out" like the clerc might tell you...
You don't "rescue" a mill dog by buying it. The millers will kill their "overused" dogs no matter what. They will continue to treat their dogs like they weren't living creatures and continue to overbreed and inbreed their dogs for quick profit. And they will just replace that one dog with another. Our rescue recently got in a female that had JUST been rescued from a mill, at 13 YEARS OLD! Can you imagine that poor girl having to live in a small, filthy metal cage, with bars on the floor so the uring and feces will drop through, only ever taken out to be bred, and producing litter after litter for 13 YEARS!

That is beyond horrific!
And that is the situation your dog comes from. And that is the business you support by buying from petstores.
The best way to help mill dogs is by NOT EVER BUYING FROM A PETSTORE! And boycott any store in your area that sells puppies!
I know that feeling whenyou see that cute little face through the store window and you just wanna take him away from there! But every penny you give to that business funds the millers and keep them going...
That's the cold, hard truth.
Here are three dogs that we recently got in, that had been dumped by a puppymiller at a zoo (!) when they were of no more use to him:
(WARNING! Some fairly graphic images!)
Betsy:
http://www.petfinder.com/petnote/dis...petid=11587593
Hugh:
http://www.petfinder.com/petnote/dis...petid=11587594
Katie:
http://www.petfinder.com/petnote/dis...petid=11587595
PLEASE DON'T SHOP! ADOPT!