I don't know about other people, but I simply will not finish a book that doesn't hold my attention. I have better things to do with my time. That being said, I found some authors I won't be adding to my auto-buy books.
I recently bought some books from new to me authors. They were all "name brands" and I had hoped to open myself up to a few new series to enjoy. Now, perhaps my mistake was buying books too far into the series...but honestly, an author should be able to garner new readers with their books and not just rely on repeat buyers.
M.C. Beaton, A Spoonful of Poison -- I simply could not muster any sympathy for the nymphomanic protagonist. What made it worse is that I had the solution to the mystery figured out by Chapter 3. I think I made it almost halfway through the book before I threw it against the wall.
Stuart Woods, Shoot Him if He Runs -- This was one of those books in a series that simply didn't have enough information about the characters. When two of the characters were inexplicably having sex (I'm assuming they had some sort of history, but it was never explained adequately), it gave me pause. AND I WRITE EROTIC ROMANCE PEOPLE. Seemed like the sex was just in there gratuitously. I had my suspicions of who the bad guy was...this one, I read about 1/4 of the book, was interested enough to see how it ended, and then threw it against the wall.
Sometimes I do struggle through a book, just because. I'm not driven to solve the mystery, but something about the story keeps me limping forward.
Murder on the Eiffel Tower by Claude Izner was one of these books. I liked the protagonist (a bookseller). In the end, it wasn't solving the mystery that kept me slogging through the awkward shifts in POV, but the budding romantic relationship and the smattering of historical details and characters.