Trader window should have category drop-down like stockpiles have to make it more user friendly
The current trade screen is definitely quite busy and hard to scan. A drop-down menu might help that, though it also carries the tradeoff of potentially turning into a frustrating clickfest if you don't know where to find something you want. I'm not sure if this is the right solution or not, but the trade screen definitely needs some love.
Perhaps a name filter that hides all the items that don't match the filter?
A filter textbox would be great too.
Or a filter for all things that I can sell, and all things that I can buy, separately. That would be a big improvement.