I read Napolean Hill when I was a mere tad. Even at the time I thought that he was pushing his points a bit much. There were a number of others in that time period who had written books about salesmanship.
There remains a whole gaggle of books about self help and selling ones self. Then there are TV personalities who do the same sort of stuff, such as Doctor Phil who is, in my mind, an unabashed hustler. Doctor OZ also comes across as a shameless con man. Many esteemed preacher men are also guilty of near criminal promulgation of hokum.
P.T. Barnum apparently had it right about a sucker being born every minute. People do buy those books and believe in the TV gurus.