If you're still not sure about buying a pet shop puppy, print out this page and bring it with you. Use the Internet to look up the breed you're interested in. You'll find a wealth of information. Be extremely careful when evaluating breeders who run ads in the newspaper.
Backyard breeders operate in much the same way pet shops do.
Money is the bottom line. Doesn't ask you questions about yourself and why you want a puppy. All purebred breeds suffer from genetic diseases, including cancer. Has puppies always available. Responsible breeders have smaller numbers of carefully-planned litters.