"I also have pointy ears, but by no means is that conclusive. It is indicative of me being something other than human, yes, but specifically a fairy? Not with certainty, no. As far as I'm aware, however, no other humanoid beings have wings such as these. You can therefore conclude, with certainty, that I am a fairy."
"That wasn't really... Wait. Are fairies the only magical beings who can shapeshift? Or make illusions?"
"...Okay, so, none of this is conclusive, actually. I can pinky swear, though!"