If you make a free sample, you better include something more than just a short introduction. When I found an interesting book in a bookstore, I usually open it in the middle. This way it is easier to get idea how the author writes and what his style is.

"A brief history" and "What's new..." I can find such things on the Internet and rewrite them. Everyone can rewrite, right?

So, what I mean is, you have to win your potential readers by your style, your ability to explain things and so on.