I found a combination of squawking LOUDLY in the ferret's ear, and shoving an offered knuckle into their mouth GENTLY cured a bity jill in a few months. Never nose-flicked. No need, as lorelei said, to meet violence with violence.
She wasn't a kit, and she meant it when she bit.
The worst was over in a few weeks. just the occasional bite to remind me after that.
Persistance is the key, mate. They'll come round.