Puppies at Pet Stores

[SharkB8]

Is there a set amount of time a pet shop will keep a puppy for sale? Say, for example, they puppy arrives at the shop, will they give it 6 months to be sold? I can't imagine they keep them indefinitely.

What happens to the puppies that don't sell? I know there can't be too many options. Open the back door, drop them off at a shelter, return them to the puppy mill? Worse?

We don't have too many malls around here that have pet shops, and I usually just go to Petsmart or Petco and only see cats for sale. I vaguely remember checking out puppies for a smile at pet shops about 10 years ago, and there seemed to be 100% turnover.

Anyone know what happens to the puppies that don't sell?