It’s hard to imagine that someone will leave a bad review on your book, but even the most universally loved books have bad reviews on them. The only way you’re not going to get any bad reviews is if very few people ever read the book.
This is not to be pessimistic, though–far from it! I’m not trying to stride in here with doomsaying and jadedness. The truth is that not every book is for every person, and some of those everypersons who aren’t a good match for your book will still be reading it. Even if you don’t deserve a bad review for simply not happening to fit that person’s tastes, you will get one. And it will probably hurt, but it is not a big deal overall. Setting yourself up to believe no one will crap on your book will make you much less prepared to handle it if it does happen to you.
And look on the bright side: occasional mediocre and bad reviews make it clear that your reviewers aren’t a bunch of loved ones and sock puppets.
My favorite one-star review is the one where the reviewer calls my book “garbage,” urges readers not to waste their money, and says I should not be writing books. Sometimes I go look at that review and giggle, because someone on this planet thought this was a worthwhile sentiment to type up.