Guidelines published by the United States Federal Trade Commission detailing when a clear and conspicuous notice is required that an endorsement of a product or service by a third party, such as a celebrity or “influencer” is in exchange for a fee or other benefit. The FTC states that it considers an endorsement to be:
any advertising, marketing, or promotional message for a product that consumers are likely to believe reflects the opinions, beliefs, findings, or experiences of a party other than the sponsoring advertiser, even if the views expressed by that party are identical to those of the sponsoring advertiser.
The guidelines are expansive as to what can characterise an endorsement and where it can be found, for example including blogs, social media posts, etc.