I got my snake from petsmart and don't entirely regret it. We had a discussion on Petsmart semi recently, and I truly admire them as a company. I think they abide by really admirable practices, and aside from cohabbing the snakes, I think they exhibit good husbandry.
I would like a second corn snake and don't intend on going to petsmart, just because I would rather fund the smaller businesses of private snake breeders. Also, you know the history of the snake, which is something petsmart can't provide (I can only guess as to mine's age) At the time I bought him, I wasn't aware of how to even go about buying from a breeder. Now that I have the resources for doing so, I'll go that route.
Good luck!