It’s always a good idea to submit for unpaid reviews first. If your book isn’t accepted for a non-paid review, you can always go back to the same reviewer and pay for a review at a later date. Paid reviews are still non-biased, honest reviews. If the review is unfavorable, you can opt not to publish and share it. Please note that Kirkus specifically often offers discounted reviews, so sign up for their newsletter. The major trade review outlets are: Kirkus, Booklist, Foreword, Publishers Weekly, and Library Journal. We recommend working with your publicist to submit your work to all five, first traditionally, and then paid for those outlets that do paid reviews: Kirkus, Publishers Weekly’s Booklist, and Foreword’s Clarion Reviews.