So here's the thing, I've been reviewing for a couple of years now and while I do, absolutely, LOVE it, it does have it's downside. Each and every time I get an review request from an author, I am thrilled. I feel honored to be offered the opportunity to read a project that said author put their blood, sweat and tears into. Do I accept all requests? No, I do not. It may be for various reasons such as genre, length, my current schedule, etc., etc.
It's when I do accept, that's when it can get sticky. For the longest time, I would finish a book, come hell or high water, even if it became painful to continue page after page. I felt like I owed it to that author to see it to the end. I don't really believe there is a truly right OR wrong way to handle such situations and I think each reviewer has the right to set their own personal policy. Mine, however, has since changed and I have to say, since making the change, my respect for authors has grown, ten fold.
I am all Kindle so I speak in percentage, lol, and I have a 25% policy. Is it set in stone? No but it's a general standard of mine. If I can't connect by 25%, I stop reading. I personally feel that is best for both me and the author because if I "force" myself to finish, you can pretty much bet on a harsher review. It's only human nature to get pissy when forced to do something you don't really want to do, is it not? That isn't fair to the author. I don't want to inadvertently unleash my "wrath" because I'm pissed off about hours of mind numbing reading that I'll never get back. For me, the best approach is to stop and give said author my reasoning.
On the other hand, I can see why some authors would feel slighted by that logic. They gifted their book to me for review, the least I can do is finish it right? And because I can see that side too, I give authors a choice. I can simply mark it "dnf" and call it a day, OR, I will honor the review request and finish the book as well as post an HONEST review.
I may not fall in love with every book that I read but when an author can take it as the constructive criticism that it's meant to be, imo, everyone wins. It shows this author is a professional and understands this world and has the balls to play in it anyway. It can't be easy receiving an email from a blogger/reviewer that basically says "Yeah...no." I feel that it all comes down to mutual respect.
Just my two cents though...