> A basic truth-in-advertising principle is that it’s deceptive to mislead consumers about the commercial nature of content. Advertisements or promotional messages are deceptive if they convey to consumers expressly or by implication that they’re independent, impartial, or from a source other than the sponsoring advertiser – in other words, that they’re something other than ads. (...) As the FTC Endorsement Guides establish, advertisers’ use of third-party endorsements may be deceptive if there is an undisclosed material connection between the advertiser and the endorser – one that might materially affect the weight or credibility of the endorsement
https://www.ftc.gov/tips-advice/business-center/guidance/nat...
https://www.ftc.gov/public-statements/2015/12/commission-enf...
These rules are enforced. For example, Machinima recently settled with the FTC over the fact that Machinima paid endorsers to include footage of the Xbox in reviews and commentary.
http://www.theverge.com/2016/3/17/11254260/machina-settles-f...