chess.com policy
For your first question.
https://support.chess.com/en/articles/8566476-how-do-ratings-work-on-chess-com
For your second, the vast majority of players and games are played fairly. However, discussions about cheating, potential cheating, or cheat detection are not allowed in the general forums. If you want to discuss join the following club.
https://www.chess.com/club/cheating-forum