As the New York Times observes, this isn't the first time Facebook has had trouble with contraband. There has been a rash of Facebook groups dedicated to gun sales, and the social network's community-based approach to group screening has limited effectiveness in private selling groups where members are unlikely to report violations. Marketplace isn't supposed to have that issue, but it's evident that Facebook is still relatively new to reviewing sales itself -- the months-long rollout for Marketplace may be necessary to ensure that violations are few and far between.