Since before I even published my first book, it's been branded on my brain that it is taboo for authors to respond to reviewers. Many won't even read their reviews. I think thats smart to some degree, but I do read all of mine. I like to know what people think. If it's something I completely disagree with, I let it go. But if it's a valid point, I learn from it.
For the most part, my reviews have been positive. I've yet to receive a really awful review. There was one pretty negative review a while back, but it was obvious to me that the reader rarely read romance. They just didn't understand the fantasy aspect of the genre.
I used to thank people for their kind reviews, but then I learned even that was kinda taboo. Reviewers and readers, especially on sites like Goodreads, want the ability to talk about books without the intrusion of the author....whether good or bad. Now I know things can get really nasty on Amazon...like really bad, all out scathing reviews. And for an author, it can be devastating. We put so much blood, sweat, and tears into our books...they're our babies. It hurts to hear they're not liked. Or despised...or compared to the contents of a litter box.
Recently a very popular author made some comments about a negative review she received on Amazon...or rather her husband did. Whatever. This isn't new. It happens every so often. Some author flips out and chaos ensues. Her reactions after it all went down were less than favorable. And they make all authors look bad. This is a subjective business. Everyone will have their opinion, and not all of them will be nice. You have to grow a thick skin and put on your big girl panties if you want to survive this business. And keep your mouth shut. And make sure your husband keeps his mouth shut too.