If you want to build rapport or gain someone’s trust quickly, match their body posture and position.
If someone is sitting with her legs crossed cross your legs. If they’re leaning away from you mean away from them. If they’re leaning towards you, lean towards them. Mirroring and matching body position is a subconscious way to tell if someone trusts you or is comfortable with you. If you’re sitting with your arms crossed and you notice someone else is sitting with her arms crossed, that is a good indicator that you have/are successfully built/building rapport with that person.