If you've heard of those sayings, the person you're trying to check has most likely heard it too and if that person is seriously trying to trick you, you'll be played like a fool.

And what is exactly is the point in knowing if a smile is really real. Happiness is contagious and if you start smiling, a fake smile might turn into a real one. And that's also true visa versa. If you've practiced your fake smile to the point that it appears real, you might even begin to really feel happy.