Well...GM Sin is 67 years old, so I doubt if he will start professional fighting. His franchise isn't built on lies or fables any more than any art. He is an incredibly skilled Martial Artist, and teacher. Otherwise, he wouldn't have the success he's had.
Pretty sure that 99.9% of martial artists are not professional fighters. No one on these threads have ever doubted his skills...so, not really getting that this is going anywhere.