Necro-bump, for great justice!

Also, add me to the list of people who had a similar idea without finding this thread earlier. In fact, I thought of something almost identical, with a few specifics.

1. My idea used the "multiple NPCs hosting different items" method to give it more of a market feel, and less of a pawn shop feel.

2. Instead of summoning the retainer to you for purchasing, my idea used a "buy from NPC" method. One can simply think of putting an item in a retainer's bazaar as a way of saying "Go take this to the wards for me."

Other than that, I thought up the exact same idea as you...only not as soon. I believe this is exactly the direction that the Market Wards needs to go. It has the Market Ward feel, including the use of a retainer as a sales liaison, but is more like a cleverly-masked set of mini auction houses. Brilliant.