That's the risk one takes when posting anything on the internet. Even a simple picture on insta runs the risk of assholes slamming it in the comments or it getting picked up by some 'cringe' reviewer.
I have yet to experience any real trolling on any platform, guess I'm not big enough for that at the moment. I am preparing for it on webtoon though when I start posting my mxm comic, since the site is notorious for rating bombs and commenters who are hostile toward lgbtq+ content. But it's another reason to only check comments/reviews once in a blue moon. I try to keep it out of sight, out of mind, unless I know I've got nice readers with decent to uplifting comments (like here on Tapas~).
I just self-pubbed a book this past December but I wasn't too worried about trolls. I figured if the rating does get bombed, I would try and spin it into some marketing angle. Like "This book is SO salacious, people can't even deal!" and show screengrabs of whatever low reviews it got. Sometimes a notoriously bad book can garner some modicum of fame as well, like Empress Theresa.
If you are exceptionally worried though, use a pen name! If something bombs, it bombs under your pen name. Then you can get a fresh start under another name!
As for where to get reviews, perhaps try ARC (advanced reader copy) programs? With a listing and processing fee, Hidden Gems Books will send out your story to their base of readers. They will read your book and hopefully leave a review upon your book launch. You can also find book bloggers and reach out to them if you think they will like your story. I feel these types of people will leave honest reviews since they are receiving your book for free and in the case of bloggers, they need continual content to post anyway.