It is possible to tell someone who has real problems with their gender from someone who is in it for the "KAWAII BISHIE! I'D BE SO CUTE IN YAOI" aspect.
Because you're their psychologist and know all their issues from their usage of smilies and squee, right?

Then there are those "FTM"s who have such low self esteem from either being fat, ugly, or both, that they wish they were another person so they pretend to be a boy with a different name
At least they aren't killing women and making suits out of their skin. Count your stars.