I find that especially with ball pythons if you chase them with the rodent, bump it into their head, or rub it too much on their body they will immediately turn into a picky eater, usually for months at a time. If I touch the rodent to the snake I do it very lightly and try not to push it too much. And I don't wiggle it or move it too fast or too much, once they start getting scared or back away I stop. Sometimes I'll try again in half an hour, that almost never works. Better to wait until the following evening to try again. Then if they don't hit it the next day I'd wait until the next scheduled feeding. If they are really young and you really need them to eat it's better to use a live rat pup, one that still has its eyes closed. At that age they are totally harmless and you can keep them in the tub overnight. They are almost always gone in the morning. I only feed live for picky eaters that are real young.
I'm also finding that many of my snakes creep up on the 1000 gram wall and go off of food. Once they get in the upper 900 gram range they will almost always start skipping several meals. Not sure why they do that. I actually read about it early on, then when some of my snakes stopped eating I went through and weighed them all and posted their weighs next to their tubs. And sure enough, all the snakes that are fasting are very close to 1000 grams.