I've read quite a few threads about the retainer system and changes that should be put into it and I think that based on what I read this should actually just be dropped and remade into a "menu like" interface as the AH but the actual price being asked would be on show for customers to purchase or not.
If players really "demand" a search function then I don't see the need for the wards themselves and having a background image of a market under the search interface will do the same as the actual ward itself. Now, I loved the idea SE had about the whole "get a stall, decorate it to show the items you're providing" and such but with the search in place there is no relevance for these mechanics.
To make this system viable but still diferent from the original AH the wards would still be devided into DoL/DoH classes so that people knew where to go to look let's say for a Breastplate (armourer), or a Bow (Carpenter). Players can place their Retainers on any ward but need to keep in mind that if you're using the wrong one on a regular basis other players might start to notice and start to bypass your retainer.
So the way I see it from the buyer's point of view is, get an interface pop up when characters pass under an arch/door or something and ask players which wards they wish to visit. A Name or Rank search would then be available within that ward (only) that would present the various retainers offering that item. Once that is done players then have the option to look into the various Retainer's wares and make their purchase.
I understand that this is not that much different from the original AH in FFXI or most other MOOs but since SE as stated they want the retainer system to work and will try to get the economy working without an AH this is the best of two worlds I can hope to see ingame.