Doesn't that just discourage people from participating in the economy? adding more barriers isn't going to help.

Above, it says, "Not being able to find what you need on the Auction House when you need it. (If you've ever been on a low-population server or even the less-played faction of your own server, you know how frustrating it can be to see only 12 Wool Cloth listed at any given time.)"

AH players aren't the problem. The problem is that whenever someone does a daily or a quest gold is created out of nothing. If the gold is not destroyed, such as with a gold sink, then the total amount of gold held by players on a server must increase without bounds. If the total amount of gold held by players on a server is relatively higher, then more people will have more gold to spend on more stuff. This, over time, causes the prices of items on the AH to go up relative to the total amount of gold on the server held by players because sellers are able to maximize profits by raising prices due to everyone having more gold.

The idea of a gold sink is that by creating something that many people will want to buy and then putting that item on a vendor of some sort for some amount of gold, the amount of gold held by players on a server can then be decreased (vendors destroy the gold) and therefore can be controlled and will stop or slow down inflation and keep prices stable.

Also, by allowing people to accumulate more gold than they can use, you're actually delaying the effects of inflation until they release their hoard onto the open market.

I think that an escalating auction house fee would help. Have the percentage go up as prices rise. To a maximum of 50%. Have the minimum cut percentage, then have the cut match the auction amount in 1000's of gold. An example would be a 7300g auction would have a 7% cut. and a 12,900g would have a 12% cut. To make this work Blizz would have to use this tax rate for the value of all auctions combined instead of the individual auctions. There would also have to be a mechanism to exclude the price of materials of the vial of sands and motorcycles from the price.