In addition to judging by the cover, I also tend to use the cover as a quick visual marker of if I want to read the full review. This is especially true for blog posts that mention more than one book, I just skim quickly and look at the book pictures, without focusing on the text. This backfires a good bit, since covers are just so similar sometimes.
For example, these four books?
Are really just one book about some kids who can't go outside during the day, because their parents were buried in the backyard after being on life support, loosely based on Jane Austen's Persuasion .