I am reticent to make too many recommendations of products or services because I think it’s kind of cheap, so when I do recommend something, it’s usually because I really know and like it – and think you might as well.
As a person who enjoys reading, I believe that Alibris is a well-kept secret. Alibris sells used books – new books as well, but their focus is on used books. This is opposite of Amazon, which pushes the new books but lets you buy used ones if you want.
I think I’ve been using Alibris since before Amazon started selling used books. I’ve never used Amazon to buy used books because Alibris never gave me a reason to stop using them. The books are cheap, the service is fast enough for me, and I’ve enjoyed the easy availability of many out-of-print books.
Why this is on a blog about low carb is simple: I’ve recommended that you put your mind on a diet and replace the junk food you feed your brain with something better – books are a good place to start.
Here’s what I do: when I find a topic that I’m interested in, I look it up on Amazon.com – they have the best reviews. I check the price, then go to Alibris. Usually the price for used is much better than new, and I buy it there.
Occasionally I end up buying it at Amazon – but usually not. I like used books both for the cost savings as well as the thought that there’s one less book being printed because I’m buying used – and maybe one less book that I wanted to read padding a landfill. I just bought Atkins’ book on diabetes – ‘Atkins Diabetes Revolution’ – for $1.99 – add $3.99 for shipping and it’s at my door in a week or two for $5.98.
If you haven’t read a book in a while – buy one and take your brain out for a spin. Your neurons will thank you.
Low Carb Confidential 
As I said – never had a problem with them. YMMV. Thanks for writing.
I tired bookfinder.com and it is a service worth trying – but it led me to the book I was looking for – on alibris.com…