So I received my first bad review from a reader. It was inevitable, you can't please all the people all the time.
How to handle this is the next question. I don't pretend to be an expert, but I'll tell you what I went through.
First, I was super disappointed. I want my book to be loved by everyone, everywhere. Not realistic, of course, but why not aim high. Okay, so my work is not beloved by all. Back to being disappointed. It is amazing what you can go through in a matter of minutes. I questioned whether or not I should even consider continuing writing. I questioned the competency of the reviewer. I felt miserable, angry, tired, exasperated... you get the point.
After a few minutes, I started to realize that this is normal. Even better than that, I realized that the reviewer had made some very helpful points. This is not always the case with criticism, but when it is specific, it can be used to your advantage.
Example: You stink! (not all that helpful)
Example: You stink at spelling (something specific, much more helpful)
The reviewer talked about certain word choices, mistakes, and so forth. Despite my wanting it to not be true, they were exactly right. Breathe.
I listened to the suggestions and was able to incorporate them in a revision of the book (this may not always be possible, but it was in my case). Because of this bad review, I think my book just got better!
Again, this is due to the specific, therefore helpful, feedback (still negative) that the reviewer gave.
I went from being kind of angry and disappointed to actually being thankful.
Will I always handle bad reviews like this? No idea. I certainly hope I can continue to see the help in what is provided.