There are several websites and platforms where you can find free professional book reviews:
1. NetGalley: NetGalley is a platform where authors and publishers can submit their books for review by professional readers. Readers can request to read and review books for free in exchange for honest feedback.
2. Goodreads: Goodreads is a popular social networking site for book lovers where you can find reviews from both professional reviewers and regular readers. You can also join book clubs and participate in discussions about books.
3. LibraryThing: LibraryThing is a book cataloging and social networking site where you can find reviews from a community of book lovers. You can also participate in book discussions and join groups based on your reading interests.
4. BookTube: BookTube is a community of booktubers who create video reviews and discussions about books on YouTube. You can find a variety of book reviews and recommendations from these content creators for free.
5. BookBub: BookBub is a website that offers free and discounted ebook deals to readers. You can also find book recommendations and reviews from professional reviewers on their platform.
6. Online book clubs: Many online book clubs offer free book reviews and discussions for their members. You can join these clubs and participate in their reading challenges and discussions to get professional reviews of books.
Overall, there are plenty of resources available online where you can find free professional book reviews. Just make sure to do your research and choose reputable sources for the most reliable reviews.