Reviewers have no obligation to review your book. Paying someone for their time to objectively review your book is not an ethical conundrum. It's business. And at the moment it's one way to break into the industry.
Are there scams out there? Fake contests? People willing to take your money and stroke your ego in the process? Of course. Writer: educate thyself on the business of writing. If you were starting a different kind of business, a restaurant perhaps, you would spent a ton in start up costs.
But if anyone has Oprah on speed dial, give her shout. Because she would love ROOM FOUR.