Determining whether a player is cheating (or conversely, taking a dive) can be very difficult. Can be, but not always. Between the IPR and the circumstantial evidence around Borislav Ivanov, it beggars belief that his successes over the chess board the past year or two have come without inappropriate technological intervention. Here's the latest story, in which Maxim Dlugy doesn't quite manage to put a permanent end to Ivanov's tournament career, but does get a point in the tournament and casts further doubt on Ivanov's reputation.
(HT: Allen Becker)