If you need a fresh pair of eyes to read your future bestseller, I will give you an honest opinion and fix a few grammar errors along the way. For one gig I will read up to 50 pages of text (up to about 14,000 words).
I'll read your book through the eyes of your potential reader and will focus on different things depending on your target audience. My goal is to help your book sell better.
Things I pay attention to:
story and characters believability
grammar errors (I am not an editor, I only catch these as I go, I don't hunt for them)