This can easily be solved with a Price Guide on the forums that is updated Monthly. That way, like the RuneScape prices were BEFORE the bad updates, you would know what people are willing to buy/sell an item for. The one month update would just be to see if any prices have drastically changed. But I know for a fact, that in having a price guide, people start to take it like it's a proper price guide and some item's could lose value, especially rares.