I don't like flicking ferrets and have seen them become aggressive when other people have done it. As said before feed them well first, clean your hands, hold them behind their back and under the arms, don't put them down when they get nippy. I shout no and pry open the mouth carefully if they do get hold. Daily attention is important to get them used to people. A play mate is a good idea also. Best of luck with your new rugshark