| Well, obviously it's impossible to know with 100% certainty. Some heuristics include: * Some cheaters will just 100% match the best engine moves. If a player consistently does exactly what Stockfish would do that's an obvious giveaway. * Some cheaters will be manually copying moves between the chess website and their engine; in high-speed games ('blitz' and 'bullet' chess) their abilities plummet when there are only a few seconds left on the clock, because they can't copy fast enough. * Similarly, a player who takes 5 seconds a move whether they're pounding out a basic book opening or making an inspired move in an extremely complicated situation will raise suspicion. * Some cheaters will just be improbably good for their known background. A few weeks back some billionaire beat five-time world champion Vishy Anand in a charity game (where Anand played a bunch of different games at once) which is the chess equivalent of Mark Zuckerberg outrunning Usain Bolt. * Chess engines will sometimes make moves that even the top humans fail to see. All the action is happening on the right of the board, and some innocuous move on the left of the board produces a perfectly executed forced mate in 15 moves? Some people will look at that suspiciously. Of course, a sufficiently careful cheater could cheat without triggering any of these heuristics - a player who only relies on the engine for one or two key moves can easily be undetectable. |