Most people who write books with titles like "How to be a millionaire" became millionaires by selling those books!!!
There is a fellow in Kenya who charges like a million bob for an "Annual Mentorship bla bla bla Program". It is "three semesters". A "semester" is one week - 5 days - at some hotel like Holiday inn. You get lunch, tea and lots of mineral water. Accommodation ni juu yako if you are from out of town. And of course the fellow pays for the conference room. 15 days, One Milli gone! And what is the fellow's expertise? Running such 'programs' in various countries around the world. It is not like you are paying to get educated by some Warren Buffet, Carlos Slim etc. Fellows who have been there done that!
Being "nice feĺlows", they invited me for a two day "trial period". Only that I had to pay 16k for the "trial". Of course they never saw me nor my 16k!!!
If I was a big shot investor (A billion shilling plus in stocks) I would for example pay for the annual Warren Buffet lunch which would cost me in excess of a 100 milli because what I would learn during the lunch had the potential to earn me billions. But paying even 10k to a fellow who hasn't practiced what he is preaching!!?? Hiyo asahau!!!
Never count on making a good sale. Have the purchase price be so attractive that even a mediocre sale gives good returns.