A simple solution
If the essay companies believe their claim that their material is not used by students to cheat then why not simply give access to this custom written material to the companies that write plagiarism detection software? This way anyone who has a genuine need to buy an essay can continue to do so and cheats will find it more difficult to prosper.
If there is anyone out there who is actually in genuine need of essays though? If there is then this is surely a very poor comment on the quality of university education. It would seem reasonable to believe that they should be provided with adequate teaching resources and support by their college/faculty?
Or of course if the companies don't believe their own claim they can continue to protest about their treatment by Google.