Happy people are a dying breed. I see it around me on a daily basis. No one expects the world to be in a good mood 24/7, but when you're in a bad mood all of the time, something is very wrong.
Sometimes it can be a personal reason for the unhappiness while other times it may be a business related issue. Either way it can affect everyone around you, more so when finances are a concern.
A writing business like mine is especially a concern. I strive to do the best work I can in writing because I don't ever want an unhappy client.
Now that's not saying you must do the impossible because there are limits. For example, I had a client try to request 30, 600 word articles all on the same subject due the very day she demanded them with a pay rate of $2.00 for all of them. I kindly told her I'd have to decline at such a short notice and very little pay. She was not happy at all and told me she would never refer me for work. Well, that was okay because I'm doing fine without it.
Situations like the example above are different, but when you have a customer purchase a defect item or buy something that didnt come with instructions and you refuse to explain how that product works, "It's Easier to Sponsor a Happy Customer - http://t.co/IXWJFOBHkE" rather than have an unhappy one who leaves your business and tells others about their experience.
Remember, happy customers means repeat business.