If you allow it to go too far you could lose your business entirely. Egos are a very tricky thing to deal with. Rage does nothing but tear you up emotionally inside and always erupts in bad behavior and lost relationships. Never, ever, go into a rage over the phone. If other people are screaming at you, you will either calm them down by remaining calm yourself or show them up for being emotionally unstable.
Rage is truly the result of an unstable personality trait.
It's really NOT normal. Perhaps some of you reading this are laughing inside yourself. If you are the least bit intelligent you can easily see that making a fast buck through the expense of other people is a way to live a very short life.