Summarize how levitt and dubner logically support their argument that cheating exists when there is high incentive

The writers of "Freakonomics," Levitt and Dubner, have always said students cheat - to achieve higher grades, which ultimately prove an improvement in social position. But educators have started to cheat since they have an opportunity to do this now, as their employment have rely on the performance of the pupils. Same applies to sumo wrestlers, who often cheat, as most are not happy with low salaries.