The atmosphere of Destiny really doesn't seem like the place to have a gigantic market for goods. I could see more of a trade channel where you tell people you have things to sell or are looking for something. All transactions would be done through private interactions after you find someone on the trade channel. This would make the game feel more like, " I just found this powerful piece of gear maybe a fellow guardian could use it" rather than, " I want more money for this stuff I found and don't care about."