If you mean selling Bitcoin for fiat, it means Satoshi put his identity and safety at risk. It'll leave trace for others (such as government agency) to discover his identity and maybe even tracking his location.
Whats the big deal if his identity is made public? Even if they were to figure it out, it would be made almost impossible to prove in a court of law (plausible deniability). There is a whole legal process that any government agency would have to go through to prove he is indeed Satoshi Nakamoto, and he would be entitled to an attorney. He could just say he denies it and say that he was a very early miner and that he has been incorrectly labeled as the creator.
By the way, remember that guy who actually claimed publicly that he was Satoshi? Even in a court of law under oath. No government agency has prosecuted him as far as I know.