Human battering rams
Yesterday I was cold-called by a telemarketer from the (formerly) prestigious Roundabout Theatre Company.
This morning, it was phone spam from my bank (when I told her it was okay to send me a brochure, she said, "please tell me what your business does." When I mentioned that my bank already knew what we did, she said, "oh, we just call people. They don't tell us that.")
And this Project Description from elance makes it clear that you can now easily buy inbound links to your website to manipulate the search engines. Cheap, too.
When people following a manual will do what you tell them to do (because they don't think they have any other choice) and you're willing to ignore social convention, the possibilities for spamming or manipulating systems based on trust are almost endless.