They drove a very obvious looking "detector van" around near our university halls for a few days, and a few days later every person that had a TV and no license

They drove a very obvious looking "detector van" around near our university halls for a few days, and a few days later every person that had a TV and no license got a letter, got scared, and paid up. Of course, everyone that had no TV and no license also got a letter... and so did everyone that already had a TV license!