Been largely beaten to death, but I'll regurgitate here:

Remove most of the wards. Leave Tinkerer's, Battlecraft, Fieldcraft, Tradecraft, Mender's, and maybe another.
Allow browsing/purchasing directly from select locations in each city. Purchases can be sent either to a retainer or to delivery box.
Fix the searching, allow searching by slot, filter by rank/job/etc. Add a free-text item search. Support individual display of HQ items.
Save pricing history for all transactions and provide a UI way to view this pricing history when browsing or selling items.
Retainers selling items will now no longer need to be placed in a ward to sell items. Extra payment will be required to have them placed in the wards. Further "enhanced payment" required to rent/maintain stalls, and a minimum merchandise count.
Tie "seeking items" into the global /translate search (which presumably is in progress) so that retainers can purchase items without having to hold one in their inventory. When a retainer selling an item is re-added into the sales index, immediately check for outstanding offers and sell the item to the oldest request meeting the minimum requested price.
Retainers now give a linkpearl to all players to notify of transactions. Each retainer can be configured to have specific transaction messages enabled or disabled.

Think that about covers it.