Many will get sick and die. Puppies and kitties do not have to be in this shape or be of these unknown temperaments. Nor do they have to have these terrible diseases they come with. You have no idea what you are getting until the vet bills begin to roll in. Do NOT buy from pet stores and online web sites that have no guarantees for you, and sell their puppies and kittens to the first person with the cash.
Reputable breeders screen their buyers, and vice versa.
It makes all the difference in what you get. A reputable breeder will take the pup back any time during their lifetime. Not just if they have a problem. Until the public is aware of the fact that most puppies and kittens come from these horrible mills, the pet stores will continue to sell these animals. Backyard breeders will continue to breed less than desirable pups and kittens.