Buying from a Pet Store encourages breeding when there are so many animals in need of homes. Now that isn't saying buying from a pet store is the most horrible thing ever. It depends on what store you are buying it from. If you go down the street to the family owned pet store that keeps their animals in nice sized cages, keeps them clean, feeds them appropriately, then that is a store you would want to contribute to (if you were going the store route in the first place). They may even buy their animals from local small hobby breeders. But the big chain pet stores are typically the ones that have not so great conditions and buy their animals in bulk from mills, keeping them in cramped small cages without adequate food.
I worked at a pet store in my teens. I cleaned the cages every single day and made sure everyone was well taken care of. Keep in mind that non of these animals are played with unless there is an employee there that has enough of a heart to take an animal out here and there. I was that one employee, who took an animal out just because I felt like, but no one else did. Then the pet store started selling dogs and it got really bad. They would feed the puppies expired SENIOR dog food, or anything else that was expired. They would get extra meds from the vet and if the dog looked sluggish or ill, they would just self medicate. They would break a pill into half and give it to the dog, hoping it would temporarily clear up the problem so it could be sold. I was asked to get a pill and put it in one of the dog's food, so I did. When the owner found out I put a FULL dose in there and not a half dose I was yelled at. It was HORRIBLE. I bought one of my puppies from the store (I did work there and I felt so bad for this dog) but they just replaced it with yet another poor dog. That is when I realized exactly what I just did... I just made this pet store a profit and allowed them to put yet another poor dog in the empty spot.
You know what the pet store did when someone came in to buy a DEAD rat to feed their pet snake? They would take the rat, which is well and alive, hold it by its tail and slam it over and over again onto the tile floor. I would hold my ears and run to the very opposite side of the store and just wait for it to be over. Sometimes I would go back there and you would find blood splatter on the floor that wasn't cleaned up. I was 16 at the time, this was my first job. I thought this was normal pet store stuff, I just dealt with it.
If you want a pet, look into the classifieds and the shelters first. Wait a bit and see if an opportunity because available. If you are going to buy from a pet store, be selective. If the pet store had poor conditions, don't support it by purchasing your pet or supplies from there. Try to be as selective as possible.