scrutineer

A person who scrutinises; a person responsible for scrutineering.

Those people coined the term “open source,” to stress the instrumental benefits of allowing others to scrutinize code: these scrutineers could root out defects and prevent the nefarious subversion of code to spy on or steal data from its users (there’s a saying for this, too: “with enough eyeballs, all bugs are shallow”).

A poll-watcher.

A person who observes any process which requires rigorous oversight.

To scrutinise; to thoroughly check that an election is being run fairly, or that a vehicle meets the rules of a competition, etc.