We all worry about whether registered users are "real," and in some cases it's not just a matter of academic interest.
According to the Media Guardian, online bookseller
Amazon.com has "quietly introduced" a credit-card requirement before anyone can post a book review. It's not an effort to get money from reviewers, but rather to crack down on a practice sometimes called "astroturfing" -- creating a fake grassroots movement. Because the lay readers' book reviews on Amazon.com can influence purchasing decisions, it's believed that authors and publishers have been posting anonymous reviews intended to boost their own sales while undercutting rivals.
