In my role at work in a call centre, I spoke to a customer who had lots of notes from previous calls stating they were abusive. When I spoke to them I tried to remain open minded and at the start of the call the customer let me know about the mental health problems they had and how they can sometimes get very anxious.
The call had a positive outcome and the customer was very amicable. I made no assumptions and gave them time to speak and I remained polite throughout the call. If I had assumed that he was going to be rude or abusive I could have become defensive from the beginning of the call, giving the customer negativity to react against.
People generally feed off each other’s tone, body language and choice of words. So, the best thing to do is to assume the best in every person you meet and act accordingly. The interactions you will have with people will be more productive and more pleasant.