Why Do You Buy A Particular Book?

I have often wondered what makes one buy a book. The times that gets me thinking about this is when I discover a gem that no one talks about much. They lie at the corners of the bookstore, alone, shunned while other books shine brightly to our eyes. Fortunately, through fate or unavoidable circumstances, we stumble upon these undiscovered gems and wonder, why didn't I pick this before?

I thought of a few reasons:
1. Blurb: The blurb at the back page. That is my guide to the book and the right hook there makes me pick it. And writers, well, they do a great job at it!
2. Cover page: Don't judge a book by its cover? But we do judge them, don't we? It is sad, but our visual sense is so much more dominating that our reason. 
3. Visibility: There are a lot of people talking about it. In a good way. And sometimes, if they trash it too much, even that gets me itch to read that book. (I know, weird!). Visibility, of course, is directly linked to promotions. 
4. Reviews: I depend a lot on reviews. Reviews from reliable sites and blogs. But I often wonder, how many are genuine? Especially when they are part of promotions? 
What makes you buy a particular book? Please vote and let me know! Why Do You Buy A Particular Book?