How they smell depends on their reproductive state, which will obviously vary throughout the year. Intact males can smell pretty rank when they're in season, but neutered ferrets don't really smell of anything except their bedding; our first ferret spent so much time sitting in my wife's lap that he smelt of her perfume. In general though I'd say that ferrets have a "biscuity" smell, and the darker ones a very slight smell of chocolate.  Fatuorum