1. Read this care sheet and decide if a tank is really the right set up for you.
2. Happy ball pythons do not do much so if the animal is running all over the tank there is most likely something wrong.
3. Health is hard to determine by site only if you do not have experience with this animal. You want to look at length to girth ratio, shedding conditions and the presence of parasites. The animal's feeding history is also important.
4. If you like active animals, a ball python is not a good choice for you. They are one step above a pet rock when they are healthy and happy. A rat snake may be a better option.
5. Avoid pet stores. There are many fine breeders on the internet as well as on this board that will guarantee that you receive a quality healthy animal. Most pet stores will not.