Marketplaces

What makes marketplace business models so attractive, especially as compared to classic ecommerce and retail? (Hint: network effects.)
From the classic unbundling of Craigslist to entirely new marketplaces enabled by smartphones and mobile, a16z general partner Jeff Jordan - a veteran of numerous marketplace businesses and currently on the boards of many such a16z companies - shares examples, drivers of profitability/margins/moats, and what makes marketplaces superior for consumers as well: identity, reputation, payments, trust and safety, frictionlessness, and transparency.
This video is based on a talk given in 2015.