My phrasing was poor, but they do so generally in a very good faith fashion. It's not just a wink wink rake type thing. For instance there are no fees at all on the most popular and high-volume markets - geopolitics and world events. And not only are there are no fees even on smaller markets for market 'makers' - people who put up an offer, but they provide a percentage of all fees collected from market 'takers' back to the makers, as a means of encouraging liquidity.