Seeing as though I'm learning about behaviour analysis, I can usually tell when people are fake since there are many ways and many behaviours that indicate that one isn't being true and faking. Also a lot of people who are fake will change their personalities a lot or their ways frequently as well. I've also noticed that when one is faking they tend to unconciously reveal themselves when they reply to a thread or when they post. Sometimes they say one thing in one thread and say another in another thread. For example, if they say they live in Toronto Canada, maybe a month or so later they will say Where I live in Ottawa is usually pretty cold
There are always ways to find if someone is fake or not. You just have to know what to look for.