One of my best ferrets of all time (Dooker) was a bad (to the bone) biter
that was taken to the vet to be euthanized (along with his poor cagemate,
another gorgeous male) - both 11 months old.  Thankfully, the vet
convinced her to take them to the local ferret rescue, instead.  Well, I
adopted that "bad biter" (because my best friend wanted the other one) -
and after a few bad bites, (and one or two second thoughts), we found
that Dooker had two adrenal tumors, both pumping out testosterone (his
level was 2 1/2 times the upper limit for an intact male).  It took a
couple of months for the testosterone level to drop - and then he became
the most terrific ferret in the world ... gave kisses, loved to learn
tricks, would sit up and beg, roll over, jump from the top of his cage
into my arms when I clapped my hands .... just the greatest.
 
I am with you - there are no "bad" pets - just bad owners ....
[Posted in FML issue 4419]