I rarely stop reading a book altogether, instead I skip to the last few chapters and read those so I know how the book ends. Lol, actually I've read a few books backwards because of this little idiosyncrasy.
Lol I do exactly the same! And then I will search for keywords, eg. the name of whoever turns out to be the villain, and read those parts, and that might lead me to do a different keyword... good times. My dad always started reading the newspaper from the back, and that's what I do too. Magazines as well.
Within the last 1400 books I've DNF-ed 10 of them....not bad for that many read. I should follow your lead though and at least read the last 2 chapters so I get an ending!
The American Duke by G. L. Snodgrass is one book I read that would be a good example of grammar and spelling at its worst. She has written many books that have received good reviews but is always criticized for poor editing. I know I would never read another of her books. Why would a professional author not want to do a better job?