How can I tell if a screenshot of a facebook convo is fake or not?

[..............]

How can I tell if a screenshot of a facebook conversation is fake or not? (A girl from school sent me a screenshot of a conversation she had with a guy in facebook. They were talking about me)
It was a facebook mobile conversation

[M.]

It is almost impossible to be sure, Its very easy to generate one. A few things you can check is are there ads on the right side, check minute details, thats the only way