@ysmina-- Often times, the writer himself or herself is not a psychologist. I don't think it's necessary to be an expert in this field to criticize a piece of work that has elements of psychology in it. I think a brief research on various disorders could be enough.
Fiction isn't written for experts. It's written for the regular people who want to read something stimulating, that gets them to think. We're all free to develop our own theories about why a character in a story did something. As long as we're not talking about a real person, why does it matter? And there is usually no way of confirming our theories anyway, unless the writer comes out and says that he didn't write it with that intention.
We can't limit psychological criticism to expert opinions. Where is the fun in that?