Entropia Universe uses the real green stuff, as players deposit IRL money which they can later withdraw, so inflation needs to be kept in check -- otherwise the whole company may bankrupt in an instant. The solution for Entropia Universe is to forge new items with an average value < the average value spent to create/obtain the items. This is the same type of system you find in gambling: ROI < 1:1. (The surplus pays for development and owner dividends.)

If you run with this in a normal game (without IRL cash) you need to keep track of the total value in the system. Then you ("the Treasury") can choose when you need/want to create more value in the game, or do so automatically if the value drops below a certain threshold.