After an article is published, it is entered into the "HubHopper" and Hubbers can Vote articles Up or Down, give reasons why, and they are able to "Flag" individual articles and Profiles.
When a Hub or Profile is flagged, the Moderators (humans who work in the San Francisco headquarters) who are trained to moderate Hubs, will make the final decision on whether or not to keep the Hub/User published.
All of this can be found within the HubPages Learning Center. Click here for more information: http://hubpages.com/@learningcenter
I hope this helps!