It seems to me the easiest fix to Market Wards is to keep the basic system as is, but remove the actual wards. Here's how I see it would work.

1: you exchange items with your retainer at the summoning bell.
2: you go up to an item search counter and check the current rate of the item you wish to sell
3: While in the same menu you select up to 10 items from your retainers inventory to sell.
4: if you want to buy something you search the item search feature and purchase it directly from that menu. They money goes to that players retainer.
5: you pick up your Gil from the retainer bell after your item sold.

this way would keep the market wards working exactly how they already do, just without the constant zoning and without searching for the retainer with the item your looking for. Also you wouldn't have to run back and forth between your retainer and the door to check the prices of what you want to sell.

I don't see how this system would work without a flat tax on all items, or perhaps different tax rates on different types of items at different cities to encourage people to go the LL and Grid more often.