The want to buy ads get flagged by CL because there are so many of them from so many users that they look like spam. A large portion of craigslist flagging is automated by Craigslist itself. All the want to buy ads are so similar they can get flagged off the bat. You can tell because they can get removed before they are even searchable on CL. It also takes multiple flags from multiple users to influence CL. So it isn't one or two greedy flippers flagging all the ads. Try flagging an ad and see if it gets removed, it most likely won't work.