At less than 29 months old, StockX is one of Detroit's fastest growing startups, employing 300 people in the city. The e-commerce company is a so-called stock market of things, seeking to commoditize high-end luxury consumer goods like sneaker, watches, handbags and street wear. StockX CEO Josh Luber and Chief Operating Officer Greg Schwartz sat down with Crain's Senior Reporter Chad Livengood recently to talk about the company's rapid growth and where it might be headed next in the evolving world of online commerce.