The service called "copyediting" corrects errors in spelling, punctuation and grammar, and edits for consistency. For example: Should you write "ten o'clock" or write 10:00, 10 a.m., 10am, 10:00 a.m.? The copyeditor will take care of such details so you can relax.
Authors might not even realize that their 300-page manuscript uses the word "just" 249 times. That's okay: You hired a copyeditor who will catch things like that, let you know, and fix it before it distracts a potential publisher or a reader. Such issues are called "style" issues, and they're bundled with BookEval's copyediting services.
Always have a second person, preferably an experienced professional, check your manuscript and page proofs for errors. The author alone cannot catch them all. I have seen books whose whole first printings had to be destroyed because they contained an embarrassing number of errors —a very expensive outcome for an entirely preventable problem.
The fee for copyediting is .05 per word of your manuscript. That includes fact checking.