Facebook Groups and Marketplace are both good examples of content graphs. Your social network is irrelevant to them, in fact you may prefer NOT to see the listings made by your friends/family as the negotiation/purchasing is often nicer when it is relatively anonymous. Facebook's one moat is very shallow in this space.
Unlike high attention media with placement and interstitial opportunities, Marketplace and Groups are not great business models.
The social network graphs of the people contributing to e.g. a local group or marketplace helps in making sure that people behave somewhat honestly, I've found. At least in locales with like < 5k people.
Unlike high attention media with placement and interstitial opportunities, Marketplace and Groups are not great business models.