Sandbagging is rife on chess.com

Discussions about potential cheating is not allowed in the general forums.
https://www.chess.com/legal/community
If you think your opponent is cheating/sandbagging, you can report them using the reporting feature.
https://support.chess.com/en/articles/8562517-how-do-i-report-someone
If you want to discuss about cheating and what can be done about it etc., you can do it here:
https://www.chess.com/club/cheating-forum