Ferrets shouldn't be shampooed too often. The more you shampoo, the more oils the ferret produces, and so the more you have to shampoo (just like your own hair).

If your ferrets do have an odour problem then look to their bedding. Ferrets take up odours from their surroundings very easily. If you keep their bedding clean and fresh smelling, then your ferrets will be clean and fresh smelling.