Keep this in mind that their play and response will probably be more intimate at home than a shelter. Their play may also be different when you get them home. Be sure to handle your ferret, but also understand that if you are nipped at the shelter it's most likely because there is so much going on that they are overwhelmed and nervous. A nip at home may never occur. Remember, older are still active but nip less if at all.
Patience is important with any mammal.
Ferrets are in need of daily attention. If this is an animal that you are interested in putting in a cage and watching it spin on a wheel, this animal is not for you or your family. They need interaction and affection as a dog or a cat needs. Well, the cat will let you know when they need you but a dog needs to be a regular part of the family.