Scrutineer
A scrutineer (also called a poll-watcher or a challenger in the United States) is a person who observes any process that requires rigorous oversight. Scrutineers are responsible for preventing corruption and detecting genuine mistakes and problems. The scrutineering process most commonly occurs alongside voting in an election. The scrutineer observes the counting of ballot papers to ensure that election rules are followed. There are other uses of the concept; in motorsport, a scrutineer is responsible for ensuring that vehicles meet the technical regulations.