The first is that most unpleasant customers are not unreasonable people. They are unsatisfied people who are behaving unreasonably. The second is that in most cases, once we take the time to fully understand why this person is agitated and behaving the way they are, then the problem becomes much easier to solve and far less traumatic. And everybody laughs and says yes, but the thing is, you should ask that question while the person is there. The customer won't feel the need then to repeat himself or herself over and over again and stay agitated.
People like to hear that.
So these nasty customers, as unpleasant as what they say or do may be, are giving you some pretty valuable information. Thank you for giving me a chance to fix it. The evaluation stage is where you can work with the customer to come up with a solution instead of butting heads. Once you come to a decision, do it. The best advice I can give an entrepreneur who has employees is not to underestimate the impact that negative customers or experiences have on performance.