I actually do think that proper handling helps a lot. If you handle them roughly it worsens the situation. You need to respect the snake, don't grab him and toss him around when he doesn't expect it, especially if they are sleeping in the middle of the day. Work with them in the evening or early PM when they are the most active. I'm actually starting to calm down one of my meanest snakes due to a mite problem, I'm putting a reptile mite spray soaked paper towel over him every few days and wiping him down. I'm trying to keep him mostly covered when I do it, he feels more secure and is getting used to being handled without snapping at me. Basically it comes down to a trust issue. If your snakes trust you then they won't be mean. I'm sure it depends on prior experience too, if that snake has been handled badly and doesn't trust people it will tend to be mean until it meets someone that it can trust and someone who will work with it to build that trust. Snakes are smarter than some people realize.