Most of us look at reviews when considering whether to buy or subscribe to a new book or film, whether in print or downloaded. So if you are an author of a recently published book or the producer of a film, getting reviews to your target audience is essential. In addition to obvious important review sites like Amazon and Goodreads, you can try writing reviewers, bloggers, journalists, and groups that may be interested in your book; however such communities of interest are proliferating wildly and getting more specialized and varied in quality, so you can easily spend all the time you hoped to spend writing chasing reviews.

Getting reviews can also be expensive. In addition to providing free copies of your book, you may have to pay for reviews. You can get help in your search for free (and hence more credible) reviews, but it often comes with strings attached. While searching for reviewers of books similar to mine, I came across BookSirens.com. The company is an interesting example of many new enterprises that have emerged to sell marketing services to small, independent, and self publishers.
It works like this: If you register as a member willing to review books, BookSirens will help you publicize and possibly sell your reviews. The attractiveness of your reviews are based on your profile on Goodreads, Amazon, or other review sites.
As a new BookSirens member, you register your preferences for genre, the types of publishers you will accept review copies from (mainstream, independent, self-publishers), formats you accept (PDF, paperback and hardcover), and whether you wish to be paid or if you will review for free.
Then BookSirens analyzes your past reviews and creates a sophisticated profile of you as a reviewer with graphs and pie charts.
The number of books you have reviewed in the past is analyzed by genre, historical period (eg Contemporary, Historical, Futuristic) and character type (eg Adult, Young Adult, Animals, Family, Spies, American, European, etc) and any theme preferences you may have (eg hero’s journey, coming of age, romance), based on the books you have read and reviewed. Then your ratings are compared to other reviewers by each of these attributes.
An astute author or publishing marketer will be able to determine whether a reviewer with one of more of these preferences is more likely to give you a positive review. There are some shortcuts to getting convincing reviews without buying them. The Frugal Book Promoter by Carol Howard-Johnson will help you make a good start: https://www.goodreads.com/book/show/12493189-the-frugal-book-promoter