GOOD REVIEWS discussion

I have a question I can't seem to find an answer for. This seems like a good place to ask. When considering purchasing a book online (or putting one's book up for purchase online if one is an author), how much of the book is generally expected to be offered for free as a sample of the content? The whole first chapter? First ten, twenty, twenty five pages? A certain percentage of the book? Does it even have to be from the beginning of the book? Hope you can help. I'm really in the dark here.

Thanks!

Smashwords encourages the first 20%

Okay! I'll take a look at my manuscript and see where 20% puts me. Thanks!