@EssExTee
There was an episode of "Penn and Teller: Bullshit" that discussed polygraphs.
Basically, they are a con. They way they "work" is that the machine is run, questions asked, then afterwards, before the subject has an opportunity to leave and irrespective of the "results", the "operator" tells the subject that the woo-woo box says that they were lying and that it would be best to admit it now.
In other words, it's all about manipulating the subject into an admission.