When you're searching online, be sure to spend some time finding out where the information you are seeing is coming from. Look at the URL (web address), the title of the website, and look at the About section for more information. If you're still not sure, try googling the website or publication itself for more information on it.
Try a Google search for your book combined with "book review". You can also search specifically for a publication known for book reviews (such as the New York Times).
In addition to the Times, which is a known publisher of in-depth book reviews, try searching for some other publications such as: