trading with retainers : add icon/border to show if item is in the other inventory

This would speed up trading with retainers a lot. I like items to stack on retainers. Currently I have to search for the item, then select retainer, open trade and trade that item s/he already had to make it stack.
If the trading screen items had icon or border showing if the other inventory had that same item, I could trade all the items that we both have on one go. I would only have to go through the retainers once to 'sync' all the items.
I would think that this is easy enough to implement and it would speed up trading with retainers tremendously.

Please make this happen!

Or you start to organize your retainers for the different types of items and use your memory which one has which type.
problem solved.

/irony off

well - as a lvl 60 multicrafter stuff accumulates. I got 6 retainers, they got 1.050 inventory slots. in AH alone there are 23 categories (counting main/off-arm as one and all armor as one). I freely admit that my mind is not up to it ^^.