I learned that if I DNF an Overdrive library book and return it early because I didn't like it, soon thereafter Kobo will try to sell me the book so I can finish reading it. I have better luck marking them finished. I still occasionally get an email trying to sell me the next book by the author, but it seems like those emails are fewer than the "buy it and finish it" emails I used to get.
Too bad when you finish a book there's no option to click "I hated this, please don't recommend anything else by this author"
