Trust is an interesting word.
When I meet people, I tend to give them the benefit of the doubt. I am hopeful, I suppose they are a person whose values are similar to mine.
However, I trust most people to look after their own interests. A SIL, for example has no concern for anyone's time (She was late for her father's funeral. As she had the first reading, she kept a couple of hundred folks waiting.)
I think where most of us feel betrayed is when we suddenly find someone we trusted to do one thing has done something else to our detriment.
Maybe that's why I'm sometimes pleasantly surprised when a person does something nice instead of what I trusted they would do.
Best
Les