Advice from the old lady: Perhaps esoteric.
The wise thing to do is observe behavior and keep your opinions to yourself. This is important in 2 different ways: A.) You do not reveal that you are actively observing or for what purpose and B.) you should be careful not to color your judgement of a person or situation based on past behavior by people OUTSIDE the situation. Doing (B) can be rather challenging.
Now before everyone freaks out...I am not saying you shouldn't retain your awareness of things you or others have observed as general behavioral trends. Of course you should. What I am saying is that all individuals fall on a continuum. A single individual therefore is NOT all behaviors with all the trends that hold true in the marketplace as a whole, but will likely be representative of SOME of the general trends to SOME degree.
So you bear in mind the things you know about women, let's say, in a general sense, but you observe the individual's behavior. You act based upon the behavior you observe from that individual rather than on your generalized understanding.
Back to your specific question, OP. Let's think about common assumptions. 1. Lies can be easy to get away with if told by a customary liar. 2. Generally honest people may have "tells" when lying. Those assumptions may or may not apply to the individual in question and the application may also vary according to different circumstances involving the same individual. Ever watch master poker players? They own manipulation of the two assumptions noted above and use that to advantage.
In other words it can be a crapshoot (which I sense from your post is your point.)
One thing to always consider is that your own past history influences sub-consciously your present interactions. Your mind is going to recognize certain behaviors and associate those behaviors within contexts your mind has previously constructed from past experience(s). Signal strength correlates to the power of the current imprint on your mind. This is why (B) above can be very tough depending on the triggering behavior (which could have an ENTIRELY different context from the way your mind sorts it.) It takes mental effort to reject the subconscious sorting and observe objectively. It is uncomfortable.
You can choose to start your interactions with someone from an assumption of honesty or from an assumption of dishonesty. I would suggest that starting from an assumption of honesty is the better side from which to begin.
There is clearly risk in doing this but there is no other way to build trust. I start out from a trusting place but observe closely and as objectively as I am able. My comfort level increases with trust affirming interactions and decreases with interactions that do not reaffirm trust. Your mind is always doing this behind the scenes.
I would submit that just as a stock prospectus will tell you: past performance is not an indicator of future results...So at the end of the day you have to decide whether or not to extend trust to someone. The purpose of my post here is merely to point out that sometimes our "gut" is a reaction to incoming data that is inconsistent with our experience generally. Other times you are responding to a trigger FROM that particular person. It can be hard to know. Work on looking within yourself to examine which phenomena is happening to explain your "gut" reaction. This requires mental energy but as you become more self aware you'll get better at it. As you become more self aware you'll notice I bet that your gut magically becomes more empirically accurate.
