To open the shop window, you have to click two times - once on the NPC and once on the dialog to choose the shopping-option. I think this is one click too much.
I would like the trade/shop window to appear immediately after clicking on the NPC, without showing the dialog. One option would be to remove the dialog entirely, which affects at least one quest, which would then need to be moved to another NPC. Another option (the easier one) would be to skip the dialog if opening the trade/shop window is the only choice in the dialog.