No responsible breeder would ever sell to a pet shop. Please never buy a puppy from a pet shop. Please contact dog rescues in your local area. There are so many awesome dogs that just need a chance of a loving home. We have no need to bring any more into the world when so many die from lack of a home every single day.
To find out more about puppy farming please take a look at the Puppy Love Campaigns website. Also Pup Aid website. Be sure to sign the petition on the Pup Aid website to register your disgust at the horrible business of puppy farming.
This video explains the issue very well.