Brennan,
I was not a polygraph examiner but I worked very closely with them, specifically in criminal investigations. No examiner worth his salt would characterize a polygraph as "pass or fail". They evaluate the entirety of the examination and the "results" are far more nuanced than flagging deception on a particular question, so indeed, examiner judgement and subjectivity is very important.
I attended training seminars where experienced polygraphers acting as test subjects employed countermeasures to try to "beat" the test and fool other experienced polygraphers. I never saw one fully succeed. When a well trained examiner proceeds through a carefully selected set of questions and follow ups, circling back to the subject matter, the subtle difference in those physiologic changes move that needle. That being said, the uncertainty and variation in skill level throughout the industry is reason enough to keep polygraphs inadmissible in court.
The true value of the polygraph examination in criminal investigations is to coax the truth from a reluctant subject. A good examiner incorporates interview and interrogation skills to persuade the subject to be forthcoming. Sometimes the stress of the test and fear of discovery is enough to elicit a full confession.
He was born and raised in the US but is a citizen of Peru since 2015.