I don't think trading will be like in borderlands where you can duplicate items whenever you want. They seem to be putting too much effort in these weapons to have people multiply them like crazy. It also makes you want to hold on to weapons that took you a while to grab. Even trading (item for item) will most likely be possible. I don't like the idea of an auction house, and I don't think we will be able to purchase the most powerful weapons. The best items should only be obtainable through lot drops from bosses.