Fear is a survival tool not a handicap.
When the customer is wrong it is not a good idea to tell them.
I cannot tolerate my bad behavior in another person for 10 seconds
Business friendly is the middle ground between being too cold and uncaring and the other extreme of being too familiar
Don't let the opinions of others define who you are. Take them into consideration, make adjustments if necessary and then go be you!
If time heals all wounds, then why are there so many ticked off old people walking around.