I’m continually stuck by how serene August appears, regardless of how Emma or Henry is reacting. For his calm presence to be so consistent suggests to me that he is neither Baelfire or harboring a dark agenda. I take him at his word when he said he’s here to help Emma believe. If he is Bae, I would expect him to seem angry, conflicted or manipulative to maintain a cover over his spiteful intentions.
I re-watched the Pilot episode yesterday and saw a new clue for trusting August’s intentions. When Emma rides down the Main Street, a crane shot lifts our viewpoint through the traffic light, which is red in that episode. In 1×10 True North, that same crane shot repeats with a green light when August rides his motorcycle down the Main Street. Since the traffic light is above the characters’ points of view, I’m taking that as a hint for us viewers. One interpretation is that the show’s writers are telling us to stop ourselves from going with Emma’s spin on everything and go with August’s.
In the preview of 1×19 The Return, Mr. Gold's paranoia about August being in SB to kill him– struck me as unfounded and delusional. Mr Gold has good cause to be extremely apprehensive with Rumple’s and his own history of abusing others. Having lived by the sword, he may die by the sword. But he fears would make him a poor judge of character and thus very susceptible to delusional fantasies.
Perhaps August is so serene because he know SB is entirely a delusional construct and only FTL is real.