As someone who has published several books, I know how hard it is to get someone to write a review on your book. I can see that it might be tempting to pay a service to solicit reviews. It is hard to garner attention for a new book, and certainly having positive reviews can help especially if you are selling on Amazon. But paying for reviews certainly seems disingenuous to your readers. There are many legitimate people online who will review books, including a multitude of book bloggers. As with all other things in the self-publishing world, there are no shortcuts.