I am afraid of how this will actually turn out. I think the biggest problem is going to be sorting the signal to noise ratio: women's fashion is ephemeral as well as seasonal. Items people want will be in perennially short supply, and items that fall "out" are going to jam up search results. How do they plan on keeping the most relevant content in stock? If they know, tell them how to get F21/Zara/H&M to do it as well, because they sell out of a lot of things quickly.
The user experience for this could get bad fast when a new user signs on to trade their month-old H&M+<insert expensive designer> collaboration and finds nothing but a bunch last summer's Forever 21 shirts with cheeky slogans. That doesn't look so good. It's like going to the video rental store ten years ago and having them say "Whoops, we're all out of that new release, but we've got a few copies of Groundhog Day!"
The user experience for this could get bad fast when a new user signs on to trade their month-old H&M+<insert expensive designer> collaboration and finds nothing but a bunch last summer's Forever 21 shirts with cheeky slogans. That doesn't look so good. It's like going to the video rental store ten years ago and having them say "Whoops, we're all out of that new release, but we've got a few copies of Groundhog Day!"