How do you know if someone is cheating with a chess engine?

i was playing someone with half my elo and they absolutely destroyed me! When i checked the game review, they had a accuracy level of 98.6 and no blunders which surprised me for an elo of 200

[removed -- MS]

Maybe see his other games and then take actions

UPDATE : he is banned now 😂

https://kaleidoscopic-macaron-49d99c.netlify.app/

Its not foolproof but you can get an idea

This person, who you played is almost certainly a cheater. It's not just about the 98.6 accuracy. There's much more to it.

Discussions about cheating, potential, cheating, or cheat detection are not allowed in the general forums.

If you feel another member is using disallowed resources you should report them.

https://support.chess.com/en/articles/8562517-how-do-i-report-someone

In addition, publicly posting suspicions is not allowed