StockX, was created for probably the most unique reason ever, to give the $1.2 billion (U.S. only) sneaker resell market the opportunity to reliably understand the actual value of their investment in a pair of sneakers, and sell them.
Besides the need for sneaker heads to have real-time data on the value of their sneaker from a centralized source, StockX also provides assurances against fakes, which is not something eBay is known for. At the moment StockX is not available for international users, but with a further $6 billion resell market in the rest of the world that will probably be likely to change in the near future. (Update!!: as of November 2017, StockX now ships internationally :D)
The founder of Campless and StockX, Josh Luber, wants to help the sneaker resell game move closer to the stock market than the drug trade which it was/is very similar to from a market dynamics perspective.
Check out his TED talk (below) about the sneaker stock market then head to StockX to start playing the market.