How about a small tax on the items selling price if it isn't sold for a certain amount of time? I am pretty sure an Auction House wouldn't like to hold onto someone's items for a long time right? The tax on the time is also a way to keep some money out of the game. If it does not sell, the House takes money and if you run out, it wont be up as an offer anymore.
If not that, maybe a tax put on the item when putting it in to sell based on how much your selling it for? With this, if the item does not sell in a certain amount of time, the cash is "collected" (taken out of the game). If the offer does sell, then the player gets the money back because the house did not have to hold it for long.
These ideas just came to me because of the thought that people want compensation for their work. In this case, the Auction House.
23-May-2014 21:36:49