I ran across this article by accident, which describes a very bad experience by one author who hired a company to promote her latest publication. The author is Linda Formichelli, and her latest work is How to Do It All: The Revolutionary Plan to Create a Full, Meaningful Life - While Only Occasionally Wanting to Poke Your Eyes Out With a Sharpie, which sound a lot like something I ought to read, but isn't. For one thing, I already have a meaningful life, and if my life gets any fuller I don't think I'll be able to stand it.
Linda contracted with Insurgent Publishing to promote her book from ground zero into the NYT Bestseller stratosphere, which didn't happen. The entrepreneur in question, Tom Morkes, denies responsibility and wrongdoing. Linda doesn't agree with that, which you can read all about in two posts: Brave Author Outs Marketer Who Messed Up Big Time and How One Author Got Ripped Off and How You Can Avoid It.
Speaking for myself, I wouldn't have done any business with Insurgent Publishing, for the simple reason that I can't find a mailing address or phone number anywhere on their web site. Another item I can't seem to find is a long list of testimonials from grateful authors and their contact information. In fact, testimonials seem deuced hard to come by.
The real procedure that should be used with any promoter or advertiser is this: Listen to their presentation (their spiel), and get a number. In the case of a book promotion, it's the number of books the company will help you sell, or cause to sell, if you use their service. If you'll just sign on the dotted line... Then get the cost. You summary is, "So you're telling me that if I spend x dollars with you, my book will sell y copies within the first 90 days of its release - and I need do nothing more than hand you x dollars and a book that's ready to publish." As soon as you get an affirmation, put a caveat on the end of the agreement. "I'll tell you what - if what you say is true, I'll pay you twice what you're asking. And by that I mean you, personally. But, should sales fall short of the promised number, I owe you nothing."
Watch them back off.