Have you ever gone somewhere selling an exceptional product only to be put off by rude and/or cavalier employees? I have. And I can say unequivocally that I will not return. I won't complain. I simply won't return. To me, customer service is a prong of professionalism.
As writers, we are selling a product. Like other branches of the entertainment industry, a writer has fans excited about their work (hopefully). Some are more zealous than others. Yet, nothing will turn off a loyal fan faster than an author who acts as though dealing with fans is beneath them.
To my way of thinking, professionalism includes a good dose of common courtesy that extends beyond agents and editors. We, as professionals, should be considerate to our readers (including book reviewers). After all, readers want to be in it for the long haul too.