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There are obvious patterns, like the time to make a move.

Additionally, chess engines make moves that don't really make sense to humans because they are making considerations hundreds of moves out, so if a player, through multiple games, consistently makes moves that are the best or close to the best engine moves, but don't really make sense, that pattern can be analyzed.

One fluke of a brilliant move that obviously doesn't mean anything. But if you are consistently playing 1000 moves ahead, that's obviously impossible.

Combine that with user reports to see what players to deeply analyze it can work well.

It helps to consider that computers are significantly better than humans at chess, so much so that they would say the best technical move is one that looks like a blunder to most players, including professionals.