That is why we check out their credit history. Some people cheat in sports because they are embarrassed to do poorly. That is why we have referees and umpires. Some people cheat in competitions because they want to be considered the best. That is why we have reviews and investigations.
Some people cheat on letters of recommendation because they want to help a friend.
That is why we rely upon those letters so little. Some people cheat on traffic laws because they forget or do not know the rules. That is why so many signs are posted and cameras are mounted above a growing number of traffic signals. Some people cheat on anything because they believe others are cheating and getting an unfair advantage. That is why a system has to be trusted by those affected.