Is there a market place (not the one on this website) that is entirely dedicated to content trading, where people can advertise their writings in categories ? Say I want to write very pro articles on one specific industry, is there a place where I could find the people who want to buy the same specific articles ?
You could try Constant Content. Personally, I wouldn't though--why go to a place where you automatically have competition? The smartest thing to do is think about what NON content services providing place your customer is hanging out in and hang your shingle (unobnoxiously) there.