True, which is why if you're going to try to game the system, you might be better off spending that money buying multiple copies of your book along with a few selected, sustained best sellers. Then when someone looks at the best seller, they your book listed as something that other customers also published.
Create a So you'd like to... guide with your book on the guide. Make the guide relevant, not just an excuse for self promotion, and people will actually use your guide. The more people who click into items from your guide, the more Amazon will display it.
Create a Listmania list with your book on it. Again, make it relevant and you'll get better results from that list.
Make search suggestions that are relevant and accurate for your book. "You can specify the search for which you think the item should appear, along with your explanation of why it is relevant. Once approved, we'll show your suggestion in Amazon search to everyone."
Participate in Amazon's Search Inside! program.
Add descriptive content to your book's Amazon listing.Ditto for adding a cover image.
And one that I've been too busy (lazy?) to use, participate in Amazon's blog program, AmazonConnect.
These are all much longer-lasting ways of improving the sale of your book on Amazon. And they're much cheaper than paying someone thousands to game the system for you. But if people really thing it's worth all that money for one hour of dubious fame, I suppose it was inevitable that someone would offer a service to do it for them.