Good liars are able to avoid these tells and I reckon no system is perfect but the last point, trusting your gut, is probably the best as it combines a lot of conscious and subconscious observations into a judgement. I'm often unable to articulate why I trust or distrust a person but feedback from my close friends is that they'll look to me for signs about a new person we meet. You do also need to be willing to constant reevaluate and change opinions as more evidence is gathered.