You can't set boundaries with other people, but you can set boundaries with yourself.
Know ahead of time what you will and will not tolerate, and how you deserve to be treated. Trust yourself that you will respond accordingly in your own best interest as needed. For example, if a person does _________ , I will react by ____________ without feeling guilt or shame, and if the behaviour happens a second time I will _________ .
In that regard you are identifying your own boundaries of what is or is not acceptable, and learning to empower / trust yourself rather than other people.
I've never "trusted" others. I only trust myself that I will do the right thing if they try to screw me around.
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I never give you my number, I only give you my situation.
Beatles