Hatchlings shouldn't refuse unless something is wrong -- either husbandry, or not being offered the same prey items as the breeder. When they get older and approach breeding age, they are more likely to go off feed.

From what I've observed, you offer less often during a fast so that a refusal doesn't become habit. So, if you offer once a week and they refuse, you wait two weeks before offering again, and then three weeks if refused again, and so on. But only for older ball pythons. I personally haven't had mine go off feed yet, so you'll probably want to wait for someone with experience to confirm.

Fortunately my BP isn't a picky eater -- she'd probably eat a chick if I gave it to her, but I don't really want her hooked on chicks when I have so many rats lol.