You know that claim made by many of those flim-flammy book publishers when they "spam" mail you all those ads? "You won't risk a thing, just return it marked "cancelled", and you'll owe us nothing!" Well, I just did that, and it cost me TWELVE DOLLARS to UPS the book back to them. Lesson learned? --Unless you are really panting to know what is in a book-don't ever order one thru the mail! And you know what makes me even madder? That Spam publisher probably did not spend three-bucks to get it sent to me!
Reputable book sellers these days usually allow a sample download or online sample for a try before you buy feature. Amazon and Smashwords do this as an advantage for readers and authors. But you are right that there are plenty of scammers out there. I make it a rule for myself to never order from a site that doesn't provide a sample.