When trading items, you need to move them one at a time into the trading slots by selecting the item and using the mouse to maneuver it into the trading slots. This can be a bit time consuming, especially when the trading slots get full and items tend to overlay ones that have already been moved. Suggestion - when trading, right clicking on an item in the inventory should have a "barter this item" choice. Similarly, right clicking on an item in the trading slots should have a "return to inventory" choice. This would speed things up considerably.