They are actually worse than a coin toss.

The TV news show, "60 Minutes" tested several companies that provided polygraph testing services.

The show claimed some one stole some equipment. For each testing service the show said they suspected a different employee. In every case, the polygraph operator claimed they detected deception in the person they had been told by the show was the person already under suspicion. Polygraph is total bullshit, just used to add a pseudo-scientific shine to prejudice.