There is numerous reasons why this baby bp could be snapping at you.

1. The pet store could have not taken care of them the way they should be...ie...temps, food, humidity, handlying roughly.

2. All bp's get stressed moving from one home to another. As this snake may have moved more than once getting to the pet shop and not even being able to acclimate there because of people tapping on glass, and reasons stated above.

3. The BP just ate, remember that, one thing, you shouldn't have moved the BP the day that it fed, Ball pythons need a nice warm area where they can digest their food in peace.

Let this BP acclimate to his new home. Make sure you have to hides, warm and not, humid and not. And make sure your levels are all good and steady. What kind of setup do you have?