What is the lesser or two evils, getting or giving a DNF or a low rating?
I guess this question is aimed at authors than us readers. The impact of these unsavory feedback are more felt by our writer friends than us reviewers. We're already aware of the 3-star debate, personally I don't think that's bad and I get turned off by authors and tours that would ask for 4 or 5 star reviews only. That's censorship and if one doesn't want medium to bad reviews, then they shouldn't be in the business of writing books for public consumption. But let's save that for another conversation.
On to the topic at hand!
If I were to choose, I think a DNF (Did Not Finish) is kinder than a low review. To me, giving a book a DNF stamp is straightforward; I didn't like it or it's not for me. Then I would share why it didn't work for me and hopefully I was/am constructive about it. I also don't give ratings to books I didn't finish to be fair to the author and to avoid hurting their average rating. After all, I didn't read the book in its entirety therefore my experience about the story is incomplete which makes me unqualified to give a holistic opinion. To me I just think it's a good compromise.
As for low ratings, I do agree that it's unavoidable and maybe even necessary sometimes. I can be a masochist and torture myself to reading a story through even if I know that I won't like it. Case in point, the last Sookie Stackhouse novel, Dead Ever After. For that particular instance, I know that I will be disappointed because the last couple of books leading up to it were mediocre at best but I needed closure so I plowed through. Overall the trainwreck analogy applies to books that I gave low ratings to, sometimes it's so unbelievably bad I can't fathom how it got printed and released for public consumption in the first place.
So that's my opinion on the matter, I'd rather get/give a no-rating DNF than a low rating. Now I'd like to pose this question to current and/or aspiring authors, which is the lesser of two evils IYO?