Forum:What's the difference in skill between a proffesional and a non proffesional?

I know money draws the line on the term professional, but just how good is a "professional"? In another way, you can call them mercenaries, or sellswords who fight in exchange for money. Would people who fight for fun be considered someone with weak skill, or there talent has just yet to surface? If two professionals were to fight would it be anything but different if two brawlers who without pay were to fight? If that fire were so wide spread then I would be the first to jump into the raging inferno.