Why should you by an animal from the SPCA not the pet shop?

It wont matter where you decide to buy your new pet. But I find that if you are buying a cat/dog and pedigree doesn't matter you will find more choice at the SPCA. If you are looking for a pedigree then you should really go to a breeder

Pet shops usually only have a few kittens/puppies available at any one time so not much choice... With so many strays coming in to the SPCA they will always have new animals coming in.

At the SPCA you also have the option to buy an adult dog which you may want if you dont want to deal with the responsibilities that come with a young animal.

If you are talking about birds/fish/reptiles/rodents then the SPCA most likely wont have any of those and you will be better off going to the pet shop