"In the first week of 2014, $400k was paid out to content creators", noted Valve during the second Steam Day (summarised on Steamdb) - those content creators being people like you or me who belong to the Team Fortress 2 or Dota 2 communities.
These people make their own items to sell to the rest of the community and, judging by the numbers, sell them they do.
Valve believes many current micro-transaction systems create unhappy customers - what, really? - who end up training themselves not to spend money. Valve's solution is to let users make value for each other, and reward players who make the most.
More than 90 per cent of the content in Team Fortress 2 is created by the community, Valve revealed. More than 1 million TF2 player accounts have sent gifts, and nearly 2 million have received them.
A whopping 17 milion accounts own items created by other people, and there's a colossal pool of some 500 million items out there. Pha-ew.
Make players happy and you will make more money, insisted Valve, evidently overlooking Half-Life 3 and how happy that would make us all. Micro-transactions don't have to cost the happiness of your users.