First a great thanks for the retainer/search system for buying and selling itens.
In my opinion its fair , safe , pratic and easy way of economy flow for a mmorpg.

To improve the experience of economy my sugestion is:
I really miss the history/chat-log when i talk to my retainer and get my money , don't really know (can't remember sometimes) what item did he sold.
It would be a great tool for control your own economy and history of prices of your itens.

SUGESTION : HISTORY OF SALES OF YOUR OWN RETAINER.