Bad review, snarky email, it comes with the business. Some people will love your books. Others will scratch their heads and think, "WTH?" And the public criticism of your books will come. It might be a small suggestion, or something large and very snarky on a popular romance blog. You'll want to fire off a response about your book, the one you sweated blood and tears over.
Here's the best advice I can give you, and it applies to the corporate world as well. Don't ever write an email when you are upset/angry/want to hold the critic's head under water until you hear a gurgling sound. Write a letter to yourself instead.
Get on your computer and fire off everything you feel inside. Get out all those feelings, frustrations, etc.
Keep that letter in a safe, password protected file. Wait 48 hours and cool down.
Then delete it.
Time and again it's been shown that authors, even superstar ones, who take on their online critics, pay for it. The payment may not be lost sales. But it can be something everyone needs these days..something very precious...
Why waste time responding to online criticism of your books, unless you are correcting a misconception about your book? (For example, if you wrote a romantic comedy about pigs and included the fact that a pig's orgasm lasts 30 minutes and the reviewer said, "She is ridiculous! Whoever heard of a half-hour orgasm?" Then you can send a polite email to the reviewer and point out your research. You were not pulling this out of thin air, or your butt. You know the facts. BTW, pigs DO have 30 minute orgasms. Seriously. Lucky pigs!)
You'd be better off spending your time writing another book and therefore, collecting another advance and more money! If the criticism really gets to you, get together with friends, have a drink and commiserate. Then get back to what you do best...writing!
Criticism comes with this business. Readers also change their taste. So someone who loved your books a year ago may be snarking about them tomorrow with their online friends. It happens. It does NOT mean you are a poor writer. Remember, you got published. Your book resonated with an editor! Be proud of that.
And keep all your positive reader emails in a file. When you feel a little down about a bad review, pull them out and read them for reinforcement.
Be proud of yourself and your work. You're an author. Congratulations! You persevered and you made it.
Now go out and show the world what a professional you can be.