Question: has anyone ever won the moment of truth

Answer: Yes, However, one contestant in the unaired second season (S02E09) did answer all 21 questions truthfully to win the top prize. The contestant was Melanie Williams, a member of a secretive polygamist group. Most of the questions centered around the secrets of polygamy and what took place in the group in which Williams was a member. For $500,000, Williams' final question was whether she believed her father had sexual relations as an adult with a minor. She said she felt he did, and the lie detector determined her truthful for the grand prize.