Engines

When somebody uses engines, he wins.
He wins the game
Ok
But, where it is established it is late
In Addition he wins your elo and it is not fair
I propose that if he wins with engines and it is established the elo should return to the player

SORRY FOR MY ENGLISH

I remember that GM Robert Hess played a match (lost it, obviously) on Chess.com against a player who turned out to be an engine and then he got his points back...

P.S.: Lichess uses Glicko-2, not Elo.

From what I know this is very difficult to do effectively. It would be very expensive to retroactively re-calculate everybody's ratings every time a cheater was discovered and their games nullified. It's not a matter of changing one game. That game effects the ratings of not only you but everyone that you played after, and everyone that played your opponents, etc.

Simply giving a player the points back also doesn't work too well. If you have played enough games since the games you lost to a cheater your rating has stabilized again and giving the points back would make you overrated.

In the long run it doesn't matter much. Most of the players you meet are honest and the cheaters have a negligible impact on your rating.

It doesn't really matter. If you lose one game vs a cheater, play 10 more (with regular users) and your rating should be about where it was before...