MMORPG economies suffer when items, on the whole, are not consumable. The auction house, when the money goes from one player to another, doesn't help, because nothing is used up. When enemies spawn infinitely (across the whole game) and drop valuable items that are sold from one player to another, the money is not used up, so there's a natural inflation at work. In City of Heroes, salvage (AKA loot) gets used up creating power enhancements, but each player only needs a certain number of those. The rest are waste, inflating the economy, which I gather is pretty unstable anyway.
There needs to be as much consumed as there is produced per player in order to keep things balanced. Apparently Ultima Online suffered this problem too, and tried to solve it by introducing expensive non-consumable black dye tubs, which people bought and charged their friends to use. And since it wasn't used up, it really did nothing to fix the inflation, even though the vats were expensive.
Mokalus of Borg
PS - I suppose it's hard to criticise, though. We can hardly balance real economies.
PPS - As evidenced by every country's national debt.