I totally understand about the trolling used bookstore thing. I love browsing the shelves and stumbling across things I'd never have thought of looking for. It's how I get most of my reference books these days.

Plus I spent ages hearing a friend of mine raving about Melusine, only to spot the hardback in my local second-hand shop - a minor miracle here in the UK. Not so good for your royalties, I know, but it did lead me to go out and get the others as they came out.