The professional advice that I've received is that you are going to eventually get a negative review (I'm not an author; I have a business). The best way to respond to a legitimate negative review is to try to contact the person who posted it, and follow up with response with a conciliatory tone and offer another chance: "I'm sorry that the product didn't work for you. We would like to give you a new product with enhanced features. Please contact us." If the reviewer escalates, then ignore it. If the negative review is unsubstantiated, then ignore it. Those looking at online reviews with the purpose of purchasing have discovered how to filter out nonsense.
I'm not sure how that would work with a book review, but my takeaway from this is that Everybody will eventually get a negative review. If you can't deal with it positively, then ignore it.