If im chatting with someone idk, what can I ask that person that really makes sure that they are who they say they are?
By juxstaposing different things they say, you may find a clue.
You can't ask them anything that will make you completely sure. There will always be a chance that he or she is lying.
Its difficult, but if you pay attention to the little things they say or how they act or the pause it takes to answer some personal questions as in age, face book, where they live. But then again, they couldnt be lying. You never know..