"I think I did pretty well considering I started out with a bunch of blank paper." Steve Martin, comedian and novelist, author of Shop Girl
What copyeditors do:
My copyediting service includes going carefully through your manuscript with a perfectionista's eye, finding and correcting errors in grammar, usage, mechanics, and spelling (the latter generally involves detecting homonym errors--e.g. "led" and "lead"-- which our spell-check gremlins pointedly ignore). I will use the Track Changes feature of Microsoft Word to offer you a “click and go” means to instant gratification and a polished manuscript.
I do not include fact-checking in my copyediting (for example, if your nonfiction memoir mentions a restaurant located in a particular place at a particular time, I will not be checking to see whether that restaurant did in fact exist in that place and time--I leave that to the author or another editor along the way). I will, however, write you an Author Query note on every question I have concerning inconsistencies in time, characters (e.g., "Weren't Jane's eyes blue in your earlier descriptions of her character?"), and similar matters.