In the United States there is an agency which protects consumers from fraud or deceptive business practices. They voted 4 to 0 to update their rules governing endorsements, and the new guidelines require bloggers to clearly disclose any "material connection" to an advertiser, including payments for an endorsement or free product.
It's the first time since 1980 that the FTC has updated its rules on the use of endorsements and testimonials in advertising. In addition to covering bloggers, the new FTC rules state that celebrity endorsers can be held liable for false statements about a product, and all endorsements must include results consumers can "generally expect." Previously, an advertiser could cover their claims by the disclaimer "results not typical."
In this cyber era we are all prone to immediately googling a product to see what the reviews are; it's not fair that a paid endorsement may be masked as a review.