The information is basically all over the place right now and the plans for the system are likely evolving. Originally, the proposed system was definitely going to have significant restrictions, although it wasn’t completely clear what those restrictions would be. The multiplayer FAQ provides a baseline for what has been an ongoing discussion through multiple mediums about how the trade system will work:
" 1. What will the trade system be like?
Our current plans regarding the trade system are still a work in progress and will require scale testing, but are centralized around having an area for players to congregate called The Bazaar. In the Bazaar you can visit other player’s shops and purchase items for in-game gold. The player shops that appear are random so the act of finding gear that you are interested in feels like browsing an active bazaar instead of finding players on third party websites to trade with directly. We want the main item hunt to remain outside of trade so making this an enjoyable experience but not the clear best way to obtain better items is our goal. Players in a party will also be able to gift items to each other, as long as the item dropped after both players joined the party."