The only problem with having a domain name which someone wants you to hand over, and then asking for money for it, is that the prosecuting party can claim that you're a "cyber squatter".
Although, it is perfectly reasonable to ask for the price of the domain name without being labelled as a squatter.
One such case was Mike Rowe, who a while back, registered the domain name "mikerowesoft.com". Bill gates wasn't happy.