Do they not have a group of beta readers for that purpose who are happy to do it for free or trade? (kaitnolan.com)
As a writer I have a group of beta readers who help me enormously — but though their feedback is invaluable, none of them ever quite bring the perspective my agent does. (killzoneblog.com)
You can find beta readers from your existing audience, or seek them out in writers groups online. (thecreativepenn.com)