I think people on HN sometimes underestimate the importance of the middleman in economic life. You don't have to be B2C or B2B with a direct product or service. Often the most profitable position is as the switchboard.
www.airbnb.com
www.taskrabbit.com
www.twilio.com
I think we understand very well that running the marketplace is where its at. Remember, we're trying to be the middleman, just much more efficient than the incumbents.