Baiting scenarios
These social engineering schemes know that if you dangle something people want, many people will take the bait. These schemes are often found on Peer-to-Peer sites offering a download of something like a hot new movie, or music. But the schemes are also found on social networking sites, malicious websites you find through search results, and so on.
Or, the scheme may show up as an amazingly great deal on classified sites, auction sites, etc.. To allay your suspicion, you can see the seller has a good rating (all planned and crafted ahead of time).
People who take the bait may be infected with malicious software that can generate any number of new exploits against themselves and their contacts, may lose their money without receiving their purchased item, and, if they were foolish enough to pay with a check, may find their bank account empty.