Anyone who tries to tell you that markets aren't possible or efficient without the government to set the rules has clearly never tried to buy stolen credit card numbers online. From Wired:
In recent years, law enforcement groups have gotten craftier at infiltrating and taking down web forums. High-profile takedowns include DarkMarket and ShadowCrew. While those sites increase the risk of infiltration by law enforcement, they reduce the risk of being ripped off by a seller or buyer – thanks to reputation ratings not unlike those found on eBay.