Art Markman for Fast Company:

So if you're in a high-stakes situation, it makes sense to try and be more vigilant about whether you're hearing the truth. But even then, many of us look for the wrong signals. In fact, researchers have found that when we consciously try to catch someone in a lie, we get much worse at it. Our unconscious lie-detection instincts are more reliable than our conscious ones.

Oddly enough, I really thought the inverse was true.