This is a very interesting paper: 'Understanding scam victims: seven principles for systems security," by Frank Stajano and Paul Wilson. Paul Wilson produces and stars in the British television show The Real Hustle, which does hidden camera demonstrations of con games. (There's no DVD of the show available, but there are bits of it on YouTube.) Frank Stajano is at the Computer Laboratory of the University of Cambridge.
The paper describes a dozen different con scenarios -- entertaining in itself -- and then lists and explains six general psychological principles that con artists use:
The distraction principle. While you are distracted by what retains your interest, hustlers can do anything to you and you won't notice.
The social compliance principle. Society trains people not to question authority. Hustlers exploit this "suspension of suspiciousness" to make you do what they want.
The herd principle. Even suspicious marks will let their guard down when everyone next to them appears to share the same risks. Safety in numbers? Not if they're all conspiring against you.
The dishonesty principle. Anything illegal you do will be used against you by the fraudster, making it harder for you to seek help once you realize you've been had.
The deception principle. Thing and people are not what they seem. Hustlers know how to manipulate you to make you believe that they are.
The need and greed principle. Your needs and desires make you vulnerable. Once hustlers know what you really want, they can easily manipulate you.
It all makes for very good reading.
(Via Schneier on Security.)