Mark Wahlberg is an accomplished actor. And most people would expect that he would have a substantially superior command over his nonverbal signals whether he is acting or "just being Mark" - yet they would be sorely wrong. When an actor is "in their own skin" they are at best minimally better than average at fooling others.
It's important to point out that the chances of a person accomplishing a deception is proportional to the consequences of getting caught (e.g., If the "punishment" is simply a moment of mild embarrassment, then it's easily pulled off. However if the "punishment" is losing one's employment or romantic partner [or worse], then the ability for most people to convincingly tell a lie is greatly diminished).
At multiple times in the first half of this interview with Ellen DeGeneres, Mr. Wahlberg displays a partially, suppressed (and not quite sincere) smile. The example at 0:51, just after Ellen says, "Who was it?", is a great moment to examine. Notice he looks away. Maintaining eye contact during any attempt to suppress an emotional display is a recipe for failure - thus looking away is a suppression tool we all often use to avoid unwanted emotion crescendos (laughter, sadness, anger, deception, etc.).
Another similar mechanism (enhancing Wahlberg's ability to hide a full-on emotional display) is his forehead muscle which is contracted along its entire width for the duration of this video.
Of course, even if you're a film star, being a guest on The Ellen Show will still increase your anxiety level. Thus a long-duration or excessively frequent contraction of the forehead muscles may indicate a high-adrenaline state and a hyper-awareness of one's surroundings (which is almost certainly what we're seeing on Mark Wahlberg).
However during a "normal conversation" (e.g., between two friends or co-workers regarding a non-disputed topic and when neither is in distress), a person's forehead should not be contracted for such a long duration or for a large percentage of any conversation (this video is 5 min 10 seconds long). Therefore, if Wahlberg (or anyone else) were off-camera and engaged in an apparent "normal", relaxed conversation - but their forehead muscles remained contracted - then their sincerity must be immediately called into question.
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