Wow, where do I start? First off, you might get bashed a little bit for such an impulse buy. Any pet should be researched first before bringing into your home. You might be right about the poor setup at the pet store, but adding stress by bringing it into an unprepared setup is probably worse for your snake.

You may want to exchange it or get a refund from the pet store, however if it doesn't look too bad you might want to consider taking it to the vet. I would recommend that you take any new snake to the vet regardless of whether or not it looks sick, though. Many pet store snakes will come with parasites, and other problems that you might not be able to detect, so it's a good idea to get it checked out and have a fecal done to rule out any problems that they might have in the long run.

Now onto the care... please read this caresheet thoroughly. Essentially a Ball needs certain things from it's caregiver: a comfortable enclosure (a 10 gallon tank will work fine for ONE snake), a temperature gradient from the low 80s to the low 90s 24 hours a day, fresh water, and a hide on the cool and warm end of the cage. You should give the snake a full week to settle in to its environment before attempting to feed or handle it. After a week, you can try to feed an appropriate sized meal. Most pet store Balls are captive hatched (from Africa) and you will have the best luck trying to feed it a live mouse hopper. Put it in the tank about an hour after sunset for about 15 minutes. If your snake doesn't eat it, take it out and try again in one more week. Your snake will most likely eat when it feels secure and is comfortable in its environment.

Good luck!