Celebrity Endorsement
I. When Arthur Conan Doyle published the Cottingley Fairies in the respectable magazine The Strand, he put his stamp of approval on the photographs, and was likely responsible for their staying power in the coming decades.
II. Ben Franklin stepped into the smallpox debate, unfortunately spreading misinformation via major publications of the day.
III. The cigarette industry was infamous for using celebrities to sell smoking. See this advertisement with Amelia Earhart, which was intended to have particular appeal to women.