Since SoD is about throwing around wild concepts to see what sticks, how about making it so that an item bought on the auction house cannot be re-posted on the auction house. The item informational display would denote this and trading the item to another player would give them a detailed “Are you sure confirmation?” to let them know how it was acquired and that it cannot be resold on the auction house.
This doesn’t closethe loophole of selling items in trade chat bought on the auction house and that is okay because it does try something experimental to those who spend a good bit of time “playing the auction house” in an attempt to normalize that part of the economy. It might end up being enough to make a substantial difference to how the average player perceives the in-game auction house economy.