Well, what never fails is 'look them in the eye'. Not many can pass that test.
Else, leave it up to the site.
The odds are very much against this ever happening, but if you come across something really suspicious you can fill out a report ticket to bring it to Support's attention.
sftac
I'm just a starter in Chess.com when I came to a profile which was '...closed for cheating...'.
Below the sign was the 'rules'... When I clicked it, it said 'Never use computer assistance for analysing your ongoing game'. How??? How do you know when your opponent is usin computer assistance? It also said never use help from outside...etc. etc.
Basically, back to my main point... How do you know when your opponent is cheating??
Answers pls
Thanx