There are small groups of people who can trick the polygraph machine and highly anxious people get false positives. But with a good tester who knows how to adjust for these 2 factors, a polygraph can be reliable. I would heavily consider the information obtained through a polygraph test.
Polygraph is old technology and can be fooled they have now more reliable lie detectors. I only wish that they had a fool proof lie detector because it could save money in court cases just have the person accused of a crime take a test and then take him to court or let him free.
For the most part yes I believe that poly graph tests are a sight into the depth of a person's true character. Even in NCIS Jethro won't take the polygraph test when asked to take the test, so I believe it's safe to say it's kind of accurate...I know NCIS is fictitious and though there is a real one that I couldn't watch, I know the NCIS is based on the real NCIS.
I guess growing up and hearing my father daily say to me, "Don't you lie to me.", or "Everybody lies, so don't think I can't tell.", even "God says all women are born liers,." My father had many ways of saying I was born lying, and I think that is the reason I can't pass that stupid test. To this day I still have problems with verbal test. What gets me is when I know someone was lying, but they can get people to believe them. Oh right, I forgot, those are born politicians.