My 5 month old ferret is biting?

Today I got a ferret, she is a 5 month old female. The guy that was helping me at the pet store said that she was biting a lot and left scars on his hands. He said that he gently flicked her nose and she stopped biting since. I was playing with my ferret just now and she suddenly bit my hand and finger very hard and was shaking her head she broke skin but did not draw blood. Is this normal for young ferrets? Is she being viscous, playing, or is she teething? How can I teach her not to do that? I flicked her nose gently and told her no, but that just made her do it again harder and longer. Thanks