I had a similar situation with my snoopy when I got him. I could make this a VERY long story but will do my best to keep it short!
Snoopy was given to us from a local pet store (we have a good reputation with the manager) because nobody would buy him because he was always biting and drawing blood. I knew it would be a challenge (and believe me it was) but I felt I HAD to take him home.
In the beginning he was terrible and I tried EVERYTHING I could think of. Bitter apple didn't work for me and I learned the hard way that you cannot train a ferret not to bite, but you CAN train teh behavior. (hope that makes since) It is like breaking a bad habit. Here's what I found to be most effective (remember LOTS of patience!!)
Everytime Mookie attempts to bite pick him up by the scruff of the neck and hold him in the air for just a minute or two (they have a short term memory so if you do it too long he will forget why he is being punished). Boldly tell him "NO BITE" in a stern voice. after about a minute or so cuddle him and baby him so he knows he is loved. Keep doing this till he figures out the difference in attention he receives as a result of his behavior. It took a while for Snoopy to catch on, but now (a year later) having patience was so worth it, now he is a BIG love bug and gives kisses and cuddles and everything!!
When they are kits (babies) they are naturally hyper! and their skin is VERY tough so to bite each other doesn't phase them any and I honestly don't think they realize that when they bite us it hurts
Trust me he WILL out grow it, it just takes a little time, lots of love and LOTS and LOTS of patience!
Hope this helps!