BDSM games - where is the border to stop and how..

BDSM games - where is the border to stop and how to discover real maniac?
Dear friends, what do You think about the story, described in daylymail hereafter?
http://www.dailymail.co.uk/news/article-3403420/How-Sweden-s-Fritzl-used-plastic-masks-disguise-victim-350mile-drive-home-specially-sex-slave-bunker-second-date.html
Have You heared about same stories in other countries? I heared at least about Germany, USA.
Comment, please!