Shouldn't Emma be smart enough to make that distinction by herself? After using her mind reading tricks on everyone she's met, she should've learned certain patterns in behavior, choice of words and tone equal to higher likelihood of honesty or dishonesty in people. I mean, real life experts know when you're a fake ass, and Emma had a shortcut into that truth for her whole life, giving her the question and the answer at the same time with so many people that she's grown used to pattern recognition, innit?