Users may flag postings they believe to be in violation of craigslist guidelines by clicking on one of the flagging links at the upper right corner of each posting:
Free classified ads sufficiently flagged are subject to automated removal.
Forums postings and paid classified ads sufficiently flagged are subject to further review.
Postings may also be flagged for removal by CL staff or automated systems.
Funny or memorable postings may be positively flagged, for inclusion in "best of craigslist."
Of course no moderation system is perfect, and a small percentage of ads removed by flagging are compliant.
For help from CL users as to why your ad may have been flagged, visit our flag help forum, and provide detailed information about your posting to the forum participants.