If you want to have this discussion, you can have it in the Cheating Forum, not in the general ones.
https://www.chess.com/groups/view/cheating-forum
Please do not start new topics on the same thing after having them locked. The other has been deleted.
Step 1. Play a normal game
Step 2. Pay attention to patterns
If your opponent plays normally to checkmate he or she is not a cheater
If your opponent plays normally until he or she starts loosing then all of a sudden they play like Magnus Carlson, they are probably cheating.
Step 3. Ask what other people have noticed.
Seriously though... My opponent made a lot of VERY rookie mistakes which I quickly capitalized on but then his end game is completely different. Almost as if he or she had a cheat at chess app. Its a little frustrating and a disgrace to the game.