People have instincts, intuition, sixth sense, unconscious mind, all work diligently 247 to give you a reading on everyone and every situation.
If you listen to that gut instinct or intuition you will always be right and never trust a untrustworthy person. However people ignore their instincts all the time at their peril.
In business, trust is built one action at a time. If you want to start from the beginning, then returning someones phone call and being responsive to an email request are all early signs whether to trust someone or not. Remembering who they are when they call. Good hand shake, good eye contact, the way you dress from the quality of your shoes, belt, handbag are all indicators of whether to trust someone or not.
The hand shake was invented so that we could touch someone immediately on arrival and get a reading on them. The connection between the two hands connecting, creates a current, whereby everything about that person is downloaded through the link to the other person and visa versa. So whether you know it or not, there is a vibe sent. Whether you are aware of it or not you pick up that vibe and make an instant judgement about that person.
To be trusted is to have rapport. To have rapport, the brain needs to register at some level that you are the same as them, part of their tribe and thus trustworthy.
That is why business suits are wore in business. Because it is the uniform of the business tribe. You must look the same as the person you are doing business with. Look different and they simply don't do business with you.
Other more deeper ways to build rapport is the technique known as matching and mirroring.
Some easy matching you can do to build rapport is match the speed at which the other person speaks and also the volume they speak. If you misma tch those two things you won't get in rapport or fall out of rapport and lose trust with that person.
One final things, is each person has a trust convincer. Imagine a vase. When you first work with someone, they need to fill up the trust convincer vase. The first time they do something well and to your expectation, you add a bit of trust into the vase. Some people have a 4 times trust convincers, some have a 20 times trust convincers. What this means is you need to do something excellent 4 times before they trust you. Or 20 times before they trust you.
Working with someone with trust issues, means that their vase will never get filled up, no matter what you do. So working for someone like that is virtually impossible and not rewarding, as they will never trust you, which means they will always be micro managing you, can't delegate and have to do everything themselves because they can't trust anyone to do their job.
This psychological problem tends to come from childhood and worth uncovering the root cause, so you can be a better parent, better boss, better colleague and have a better life. Without trust, life is a very scary place and you can't make any decisions. You feel like everyone is out to get you.
The only person you have to really trust is yourself. Trust yourself to know when to trust or not. Your instincts have kept our species alive and well as the king of the jungle for a long long time. Trust that.