If at any point you have entertained the idea of having a ferret as a pet, and then shared said idea with your friends you have likely been asked "Don't ferrets smell like super bad all the time everyday every second?" …or something to that effect.
The truth is yes, ferrets are musky animals. Ferrets coming from the Mustelidae family, a group of mammals known for having anal scent glands. For ferrets these glands will activate when they are scared, startled, or perhaps even playing aggressively. If you purchase a ferret from a place such as Petsmart or Petco (i.e. big commercial pet store) it is pretty likely that the ferret has been both neutered and had their scent glands removed (de-scented). If you are going to run out and buddy up with a ferret now be sure to ask if they are spayed/neutered and de-scented.
Quick note: The removal of the scent glands is slightly controversial. It removes the scent and potential risks like ruptures or tumors that the presence of glands present. However, poor surgical removal and after care care can result in infection, damage to the sensitive area around the glands, and incontinence. Again… in a lot of cases this decision will have been made for you.
For ferrets the scent glands are only half of the problem. Ferrets have scents glands peppered throughout their skin that secrete musky oils. These oils are good for marking territory, or attracting potential mates. In un-neutered males the oil production will increase when it is time to start making little baby ferrets. This goes for female ferrets as well, so having a spayed / neutered ferret will help reduce the strength of their natural bouquet.
The glands around the back can be dealt with. However, there is no such thing as a skinless ferret so the musk glands in the skin stay. Giving your fuzzy slinky a bath from time to time is a good way to strip away the oils from their fur. It is recommended that you bathe your ferret with a special ferret shampoo or a tear free baby shampoo. Normal human and dog shampoos from what I gather are not recommended due to harsher compositions and fragrances.
Don't bathe your slinky friend too much though. Washing your skin too much causes your sebaceous glands to over react and create excess oil… the same goes for ferrets.
Not only should you be cleaning your ferret, but also cleaning your house. The musky oils are on their skin and in their fur when the ferret rubs his body and face on things it will transfer this oil. So keep up with the dust and oils in the areas where your ferrets play and another source of odor will be managed.
Last tip... keep an eye on their diet. Ferrets are carnivores and so good high protein food that isn't high in fat is the way to go. This mostly will effect their "leavings" but like most furry friends... a good diet comes through in their coat. Avoiding foods with high amounts of grain, vegetable, and fruit is also a good idea especially cheap pet food that is full of corn.