There are a few things that make me put a book back on the shelf and not buy it.
A: the cover
The cover of a book should get me interested in the story, maybe it is a challenge, dare to read this book. Too often, the cover is very generic and doesn’t make me curious. But the next point is much worse.
B: the back of the book
There, I want to read a blurb of the book’s location, the plot, some character names, and what they face in the story. If all I see is generally phrased celebrity reviews and stickers about newspapers or publishers book lists, my interest in that book goes down.
C: the font
Maybe this is showing my age but the smaller the font the less likely I am to read the book. For context, I sit behind a computer and read all day. Internet archive research, reading reports, writing case analyses, book reviews, all day my eyes are hard at work. Publishers I work with know that I want a manuscript or ARC in paper form, no PDFs as I need time away from the screen. And, what I read has to be eye-friendly. So, a font size of 10 isn’t for me.
D: the margin in the middle
If the margin near the spine is narrow or, if the binding is very tight, there’s the risk that you feel the need to crack the spine just so you can read the whole text. A lot of older books and cheaper publications have this and unless I cannot get that book anywhere else, I don’t buy it.
E: the chapters
Some writers make their chapters super long and others have a one page chapter. It makes no sense. The chapter size is part of the narrative flow. It is the emotional control system build in the book to move the reader from highs to a temporary slow-down before the story picks up pace again, etc.
These are just a few things that I note about a book while book browsing. What turns you off about a book?