In-store techniques for figuring out if a book is good in <5 minutes?

My natural inclination is to buy every single book that catches my eye. However when my funds or bookshelf footage is running low I try to be more discriminating in what I buy. When I'm in the bookstore I've developed a technique for evaluating books whose reputation I don't know.

In order:

1. Check the index (if it has one), skim for terms/people I'm familiar with interested in and jump to the page. Read a few paragraphs on that topic.
2. Check the ToC(if it has one), see if the chapter names stoke the same excitement that the title did when it got me to pick it up.
3. Pick a chapter and read a page or two.

I make my judgment off of that. What exactly I'm looking for in the words depends on the sort of book (and has changed over the years), but here are a few things that jump out to me these days.

1. In fiction: Descriptions of people's manners that are so vivid and on-point that they highlight the author's understanding of how people are.
2. In non-fiction concise, explicit, concrete points being made. (Recently reading Sense of Beauty by Santayana on the strength of this.)
3. Lots more semi-tangibles.

What about you? How do you evaluate a book?