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Juventus, the most successful club in Italy, along with AC Milan (only Real Madrid has won more European titles), Lazio and Fiorentina were involved in one of football's biggest match-fixing scandals that even involved politicians. These are some of the highest profile clubs in the world, and especially at the time of the scandal when Italian clubs were still among Europe's heavyweights. Italy would win the 2006 FIFA World Cup while this was all unravelling.
You may not be able to fix the winner, but in a hypothetical scenario, one or more teams can receive favourable officiating that gets them far into the tournament. This is something that may have happened in 2002 when South Korea made the semi-finals with some questionable officiating on the way. In the group stage, Portugal picked up two soft red cards against the Koreans. Against Italy in the Round of 16, the Italians had multiple goals disallowed and had a player sent off for a dive in a loss to the Koreans. In the quarters, Spain had two goals disallowed, resulting in Korea knocking them out on penalties.