When I was taking a management course, I learned an interesting statistic.
If you make a customer happy, they'll tell one person. if you anger a customer, they'll tell twelve.
That was twenty years ago. These days with all the social networks, in a matter of moments a disgruntled customer could tell thousands!
What does that mean to authors? To put it succinctly, be nice to your customers...the readers and fans. Since fellow authors are often avid readers, I'd put them on your list also.
I read something on a professional authors' loop recently (like an hour ago) that got me so riled up, I was tempted to tell a dozen people not to buy this woman's books. Of course, I wouldn't twitter it, but I could always secretly hope one of those dozen people would! (evil laugh)
Instead, I'm taking deep breaths and trying to rise above the temptation. I don't want to sink to that level. And if you believe in Karma (which I do) I won't need to do a thing. Chances are if I was insulted, others were too. Perhaps she already lopped off her nose to spite her face.
So, I'll go on my merry way, treating my readers like the intelligent, supportive treasures they are.