Perhaps achievements will cause a minor gold sink. In DL, there are "costume" achievements. In PL, for instance, they could have a "voodoo achievement," where you get an achievement for equipping a full voodoo staff set. Or a "demonic strength set achievement," etc. People will go off and buy expensive sets. Yes, lots of merchants will also buy these sets, then resell, and raise the price of these items. But when this happens, it will still drain more gold from someone else.

If these kinds of achievements are not included, I would suggest that they are.