Who's Making Money From Penny Books Anymore?

While I'd never do it, there are examples of booksellers who do make a small profit from selling penny books on Amazon.
Who are they? How.... and why... do they do it?
Here's an article that delves into this mystery:
"Can you really make a living by selling used books on Amazon for a penny?" on the Guardian.com website.
Like I said earlier: I'd never do it. But some people are making money doing it. It's an interesting read. I especially like the story of how one seller got started with free book inventory.
I'd like to try that!