OK, these are my personal opinions, others may think differently.
I would NOT buy from a petstore as I have expressed to you in another post on another thread. I have had very bad experiences with buying animals from even specialist reptile stores as the animals just do not receive the care and attention that a good private breeder will provide.
If you know of someone locally who breeds cornsnakes, then great, buy from them. Or go to a local show and buy from a private breeder there.
Personally I buy all my corns over the internet nowadays, There are some great breeders out there with some fantastic animals, who offer great advice, a good guarantee of health, shipping etc.. and a wide selection of morphs.
Rich, who runs this and many other herp sites on the web sells his corns at:
Rich's wonderful corns
Other very well known breeders are
Kathy Love
and
Don S.
I would buy a smaller one to start with so you can watch it grow, maybe a hatchling from last year.
If you buy locally you need to know what it is eating (size) and how often and when it last ate and its health record amongst other things.
Finally, snakes don't have ears, but they are good at sensing vibrations and so loud music/noise will affect and could stress the snake so this should be kept to a minimum.
Skye