I think the most compelling example of this is something called "Freemen on the Land", and related belief systems. Instead of people's ignorance of technology, it exploits their ignorance of the basics of law. Like, did you know the government holds hundreds of millions of dollars in your name in a secret account? If you just say the right magical incantation in court, you can use it to pay off your parking tickets. Many people have believed this and tried it.

If you haven't heard of it before, prepare for a journey through Wikipedia as fascinating as it is pitiful.