When I'm browsing in a bookshop, I skim read the first couple of pages, and make my decision based on the writing, not on what's going on. That being said I have a few books that I've never 'got into' once I got them home.
Charity shops are great for finding new authors / new work. It's cheap enough that you can buy a lot of books, and if you don't like them you just take them back. It's win win.
Cover art or crits won't make me buy, but it does get me to pick up and browse.
Online I read voraciously and there are some wonderful, awesome unpublished authors out there... True, it's rather a niche market, and I honestly wouldn't be seen dead in a gay bookshop - I'm out, but I'm shy as hell.
Graeme mentioned the Hobbit. I always like this from the off, though the lords of the Rings I have never, ever finished, and lord how I've tried.