What if you thought you knew someone and found out later you didn't know them at all.

... I met someone on a chat and thought I kind of knew this person only to find out this person was pretending to be someone else. Once it was explained to me I understood why this person did what they did, but now I am wondering if I know anyone from chatting.

....How can you tell? Anyone ever had this happen before? If so what did you do about it? DO you understand their point or do you not trust them again? Does anyone know how to check someone out?
I need some input here.