Common enough to merit this fascinating entry in Wikipedia for “Cheating in chess“:

Cheating [in chess] can occur in many forms [citation omitted] and can take place before, during, or possibly even after a game. Commonly cited instances of cheating include: collusion with spectators or other players, linking to remote computers, rating manipulation, misuse of the touch-move rule, and the pre-arranged draw. Many suspiciously-motivated practices are not comprehensively covered by the rules of chess and so, on ethical or ‘moral conduct’ grounds only, may be judged by some as acceptable and by others as cheating.

Next question: is there an “optimal level” of cheating?

Why cheat?