It would be a great idea to ask the owner/manager of a pet store where the puppies/kittens they have come from. If they tell you they come from breeders I would walk away. Especially if they are trying to sell you a Cockapoo, Labradoodle or any other of the fancy mixed doggies. They are not breeds. They are a mixed pup usually born in a place made for making money. These places, as aslan mentioned, do not care about the dogs they have. They care about the money those dogs can make them. You can find the exact same puppy at most shelters for a whole lot less money than pet stores sell them.
However, there are some pet stores that have paid attention and listened to the news and/or their customers and know now the serious issues some of these puppies can have. They are starting to say no to the puppy mills and instead will work in conjunction with a shelter. They may have puppies, kittens, cats, and dogs waiting for adoption taken right from a shelter. The
shelter then get the proceeds from those sales. Those pets are ok to buy.
Please do your research and ask questions before getting the first puppy or kitten you see in a pet store. Or, better yet, go to the shelters or a rescue and adopt from there. There are always lots of wonderful, loving pets just waiting for you to find them.
And thank you for coming on and asking questions before making a final decision. That shows you will be a compassionate, caring, responsible pet owner.