Communication, intent and investigations
Tournament play asks for honesty in two directions that are easy to blur. How strictly it is enforced depends on the event's OPL (Organized Play Level), which the Tournament basics lesson defines. Players must communicate honestly about the state of the game with their opponents, and honestly and completely with tournament officials (TR 501.1 and TR 501.2). But they are not required to help an opponent play, so you do not have to warn someone that an attack into a unit with Tank is a bad idea (rule 815.1.b and TR 501.3). The line is between strategy and record. You may stay quiet about what you would do in their place, but you may not let the game state or a count go wrong. Players must point out discrepancies between announced and recorded public information (TR 502.9), and anyone who notices a score discrepancy must make all players aware of it at once, calling a judge if the players cannot resolve it easily (TR 415.3.b). A player who does not call out an opponent's failure to maintain the game state, such as a missed point from holding or conquering (rule 194.1.a and rule 194.1.b), gets a Warning for Failure to Maintain Game State (TR 702.17). That error is primarily for tracking and does not upgrade, and a missed beneficial trigger of the opponent's does not count as one (TR 702.17.a and TR 702.17.b). Bluffing about your own private information is fine with opponents (TR 502.11), but never with officials (TR 501.2).
If the wrong information is spoken rather than merely left uncorrected, the penalty is a Communication Violation, a Warning for any unintentional breach of the communication policies. The correct information is supplied, and if any decisions were made from the incorrect information, the judge performs a rewind if possible (TR 703.5, TR 703.5.a, TR 703.5.b.1 and TR 703.5.b.2).
Everything above assumes the error was an accident. Errors are assumed to be committed unintentionally, and if the judge believes one was intentional it is cheating, as is abusing error remedies to gain an advantage (TR 701.1.a and TR 701.1.a.1). Cheating includes doing anything that would be a game play or tournament error, knowingly or maliciously, to gain an advantage, including trying to create errors in order to use a remedy. Lying to a tournament official is cheating, and so is deliberately failing to point out a teammate's error (TR 704.8.a, TR 704.8.a.1, TR 704.8.b and TR 704.8.c). Cheating is a Disqualification, and the head judge has ultimate discretion over it (TR 704.8 and TR 704.8.d).
Here is a worked example. A judge sees that a player's mandatory trigger was missed, and the player gained from missing it. The first question is not "what does the book say?" but "was this an accident?" A Missed Trigger, for example of a conquer effect (rule 383.4.c), is a Warning when the trigger was mandatory and missing it helped the accountable player (TR 702.2.e). A judge may look at a player's history or skill when investigating, but must not use it to decide whether an error occurred (TR 701.1.f and TR 701.1.g). If the judge suspects the player knew, the head judge may open an investigation (TR 704.8.a.2).
An investigation starts automatically after any penalty that results in Disqualification, and can be opened at a judge's discretion after a penalty if cheating is suspected (TR 701.6.a and TR 701.6.b). It can end in a suspension, and a suspended player cannot enter competitions (TR 701.6.c and TR 701.6.d). Players must cooperate and tell the truth in an investigation, and must not obstruct it or mislead investigators (TR 705.2.b). Reports of violations must be honest and made in good faith, and knowingly false ones can be sanctioned (TR 705.2.a). The head judge may issue a Disqualification even without conclusive proof if the integrity of the competition has been compromised (TR 701.2.d.5).