When should I report my opponent because of cheating？

Hello. I have a question. I only play rapid（10 minutes), for my connect is not very well. Now I have a rapid rating about 2300.

Each day I  meet some opponents who is cheating. When Chess.com found someone who cheating, they would send a message and give back some rating to me. Sometimes I find my opponent is strange, taking every move in a few seconds. But I am not sure whether these opponents are cheating. 

I want to know when should I report my opponents? How can I know whether my opponent is cheating?

Cheaters are usually pretty easy to spot. Report anyone that you find suspicious. If they really did cheat then they will be banned. If not then they'll be fine.

I  support you, report them............

If you choose to analyze the game after it's over, you will see that if they in fact did cheat, they will most likely have near perfect accuracy with 15+ moves. Of course, you could give them a benefit of the doubt, as they could be a GM smurfing, have studied perfect theory, or just playing out of their minds on that specific day. You shouldn't really report your opponents just because you're salty that you lost, you should do it if you're absolutely sure that they cheated.