A Hebrew/Yiddish word, often used (and spelled various ways) in English; particularly used in southern California. There is no exact English equivalent word; `operator' is maybe the closest. A gonif operates on the shadowy borders of illegality and/or impropriety, and gets away with it, and is not quite an outright crook. The word seems to combine proper moral disapproval with sneaking admiration. Reference: 'The Joys of Yiddish,' by Leo Rosten.
Seymour was an accomplished and clever gonif. He could con birds out of trees, and could figure out how to game any bureaucratic system within a few minutes.