A nice feature that alot of other MMO's have is kind of a marketplace.
I wouldnt call it an auction house in this game, marketplace would be more suiting.
Here you would be able to place stuff in different "shops" or "containers", and then foreigners would be able to have a look in these and buy the stuff.
For currency you could do it like 10 grass for sale, 10 metal scraps wanted.
Quests are not good for trading right now as you must be too specific with your request. Example: You want to trade 100 nails for 10 medium wood handles. But you need to say out of which wood they are made. Birch, firn... blah blah. Then you want to trade your saw for 10 bats. Wooden, plastic, metal? Not good.