How Do You Know When To Trust?

How do you determine trust? How do you know when someone is trustworthy; worth giving time to; investing in; sharing with? What is the silent measure and how is it gained and lost? What are the thresholds between caution and carelessness, protection and paranoia?

Short answer...  We don't, none of us do, but to not trust on even basic levels would mean the end of your life, I trust that the house I am in does not collapse, that the food I eat is not poison, that the car coming the other way doesn't crash into me...  So why do I trust those obvious things but not little things...  Well conditioning mainly but at the heart of it trust is two things coming together...  Patterns and accountability. I trust my house, my food and my fellow drivers won't kill me because it hasn't happened yet out of a large amount of experience and even if something dose happen it's so rare that it could be considered an anomaly (but for some even one time is enough to break the trust, depending on a variety of factors for a different topic). The second reason of accountability is the most reliable method of trust...  There's an expression "follow the money" which sums this up perfectly. Why does my food not poison me? Because the people providing it to me stand to lose more than me,  why does the car divers don't try to kill me? Their lives are more important than mine. Why does my house not collapse over my head? The people involved stand to lose to much if they don't do it correctly and same with all the people's jobs to keep these people accountable, they can lose their jobs and income, their ways of life.
So after seeing some patterns and following the thread of accountability also known as "what's in it for them" by lying to you they stand to gain no benefit, then your fine. If I had not such a complicated answer I'd probably be a lot richer or be a secret government agency spy...

If you want to catch a liar don't try the body language crap and eye position stuff,  it's too floored and means multiple things (like looking up is the brain activating visual information which yes could be creating a story in order to tell you back, but much more likely it's recalling things you've already seen)

If you really think someone is lying to you,  get them to tell their story in reverse order, if they made it up on the spot, it's hard to work in reverse linear, but not too hard if it's legit. It's a CIA trick.
Happy liar hunting y'all!