I recall reading about a patient with split-brain (severed corpus callosum) could tell when people were lying. It seems there are verbal and physical cues when we lie.
Yes. Not being able to detect lies is a social construction, part of culture. (And so the results reported in TFA are technically useless because everyone involved is operating as part of the unconscious "conspiracy" and so would naturally "discover" that it's hard to detect lies.)
You can tap into this with hypnosis, but it's unpleasant, like being an alien. Imagine being the only person in the room that can tell when someone, anyone, is lying. It would be pretty creepy, eh? Like Twilight Zone creepy. People would shun you. You'd have to hide the ability, eh? And so we come full circle: we all can tell but we're taught not to as children.
When they're really young their minds are not yet formed.
And children are biased to trust their parents and adults in general.