When marketplaces work and when they don't

Thanks to Uber’s meteoric rise in valuation, several startups are trying to mimic the idea of building marketplaces with instant gratification. So much so, that there is an aptly titled poem, " Uber for X", devoted to this. Though the jury is still out on Uber or Airbnb, some others like Exec and Homejoy have already failed to be sustainable businesses. Here are a few thoughts on the characteristics of marketplaces, including so-called sharing economy startups, which decides their eventual fate....