If they eliminate the nonsense of the tons of different currencies and stick to just gold/silver/copper and "diamonds" for the store-bought items (which should NOT) be tradeable. (or for that matter, if they are tradeable, not be the "best" items in-game. Example: the 110% mounts.
Well, they could always put in a new currency for the cash shop, just call them diamonds instead of zen/astral diamonds, have diamonds be cash-shop only for mounts/pets/bags and have the gold be the actual trading and auction house currency. This could in turn fix many aspects of the games trading systems, and still yield…
Solution - REMOVE ALL AD/ZEN CURRENCY FROM GAME - GOLD/SILVER/COPPER TO BE ONLY CURRENCY. PROBLEM SOLVED. REFUND ALL REAL CASH PURCHASES. NO MORE PROBLEM. AT. ALL. ALSO. TAKE OUT ALL ITEMS PURCHASED FROM ZEN WITHIN GAMES RELEASE AND MAKE THEM GOLD-PURCHASEABLE <-- INCREASE GOLD DROP RATE BY 15%