sounds like your other one was just one of those snakes that have a mean disposition. It's rare with ball pythons but some never adopt. There is a high chance it was a wild caught and just didn't acclimate at all very well to captivity.
Your current one, may need some time to settle in. For adult ball pythons it isn't usual for them to not eat for months, without any ill effects. To try an entice it to eat, there are several methods to try. If it won't eat rats, try mice, gerbils, hamsters, chicks or other small birds or rodents. Placing the snake and prey item (freshly killed or frozen thawed, deffinitely not live) into a paper bag or pillow case and leave inthe cage over night, may get the snake to eat. Braining the prey can work as well (ie cutting open the brain case so the smell of the brains entices the snake to eat). Offering smaller prey than normal can work as well.
ANother thing to check is making sure the humidity and temperatures in the cage are perfect as well. Also, find out what the previous owner was feeding the snake before you traded for it and when it last ate for the previous owner. Also find out what method he used to feed, did he feed live, fresh killed, stunned or frozen thawed? In the snakes cage or in a separate container? What day did the previous owner feed on?