I don't approve of pet stores selling puppies either, but since you're looking into a business venture and the pups come with the store I would go ahead with the purchase. Pet shops today do pretty well, people will buy everything they can for their pets. To pass on an opportunity to start a business would be ridiculous since you didn't bring the pups in yourself. Like was mentioned...screen your buyers carefully, make it mandatory to "sleep on it", and make them sign a contract to spay and neuter . Once these pups have good homes you can start working with shelters. Our PetSmart does this on weekends, they have a shelter come in with pups, older dogs and cats. They get walked around the store to advertise them and they've found many new homes for these animals. The shelters sell with a spay/neuter contract and don't get their new pet for a week to make sure the people really think it over. The people also sign that the shelter gets the animals back if the buyers do change their minds for some reason. It works out great because most of the people will sign up for puppy classes or for ordinairy classes depeding on the age of the dog.
I would say to go ahead and buy the business. I would love to own my own pet shop myself.