They cost a lot of money ...
As it says in plain English >> "Our Editorial Assessment evaluates sections of your manuscript for its editorial quality and publishing readiness. A portion of your work (typically the first chapter, or about 1,700 words) will be edited to provide you with a specific sample edit. You will also receive a general overview of your manuscript and constructive comments towards improving your writing and book."
The bold is mine, and as we keep saying, fixing errors is not the job of an editor, they only advise, and usually only on the story. Usually, though, if there are so many errors in a manuscript, it will not have been taken on in the first place. The OP in this thread is another reason it would not have been taken on, unless cash changes hands.
The minimum charge for it is $2,300 ... But you are able to read the descriptions of them yourself, so why are you asking?
Indeed, just as I said
But to be honest, I worked that out wrong. Min charge is £230. Still not cheap though, because 5,000 words (default charge) is not a lot.