Just my little bit o' input.  I obtained two new ferrets from a shelter
last spring, on of which was a real bitter.  We managed to break her of
this by bitting her back.  We would grap her and firmly bite on the scruff
of the neck.  This took care of it in about a week.  There is a draw back
to the flipping of the nose.  They are smart enough to associate that with
your hands and they soon learn to fear your hands.  Sometimes even enough
to cause them to nip every time you get close to them with your hands.
 
Just my experiance.  Take it at that.
 
Darin Ries
[Posted in FML issue 1283]