I'm okay with sample chapters for fiction, but have a real problem when it comes down to sample chapters for non-fiction. In a lot of cases, they will only include the prefactory material and maybe chapter 1 (where the first chapter is often a second introduction). I'm sorry, but that is not a representative sample of what they're selling. It is also a far cry from how I would preview a non-fiction book in a book store, where I would flip to the chapters that interest me to judge the quality of writing.