You had a balanced attitude, and understood the dynamics of dealing with the public. There will always be situations that test your resolve, but usually if you're upbeat and positive, your day turns out much better. I think the key point you made is to not "write off" a person, because they don't necessarily respond in a way that you prefer. People are complex beings; and most of the time, we can find some sort of common ground with our fellow man/woman to all get along.
Your comments above should be xeroxed, and handed out to every sales associate, as part of their new employee customer service training.