Many other MMO's have this feature. Why not WoW?
Auction house goods are being taxed at a rate of 5%, and so should services. Since a greater portion of the economy now involves services such as carry runs, it is now time for service providers to pay their fair share of tax, just as goods sellers do.
I propose that when a player trades gold to another player, there should be a fee of 4% on the gold traded, slightly lower than the AH fee. This would not only combat inflation but also keep in line with existing taxes in game.
Do you think WoW needs a tax on services like this?