This article is a couple of years old. It's an interview with AbeBooks co-founder Rick Pura. They found a need and solved it.

"We went to the booksellers conventions, and we passed out our brochures and sent them off to whatever lists of booksellers we could find. And, word of mouth spread on the Internet fairly quickly."

http://www.practicalecommerce.com/articles/233-AbeBooks-com-...