In the merchant window, make sure the \"sell\" button at the top is checked, then highlight \"Items\" on the list. It should show what you have that is salable. T
Took me a sec to realize I had to actually click on the \"Sell \" button at the top when I first started. I was used to being able to see everything in my inventory and just sell it by dragging, or clicking a sell button after highlighting something in my inventory.
Devs might construct a better more intuitive way to trade later on though.