I came here to say exactly this. Whoever was in charge of their video design failed majorly. The constant head shaking was very disconcerting to me and I felt like he had no confidence in his own product.

I thought the same thing, it was seriously distracting for me. Its kind of amazing that they gave him such little direction about his body language.

Yes, seriously it wouldn't hurt the guy to smile to actually make me even want to believe him.

Had to re-watch to see it, but you're right he is shaking his head, a classic unconscious behavior meaning he probably doesn't believe in it.

Maybe not - it might be derived from an Indian head waggle? That is much more neutral-to-positive than "no".