Yeah, there's actually an old sports betting scam that works similarly. You send out letters to tons of potential gamblers saying something to the effect of 'The <team>'s games are fixed and I've got the inside info. To prove it, I'll predict the winner of the first n games' Then each week, you send half the group one prediction and the other half the other. Whichever half was wrong, you ignore, and the the 'correct half' you repeat with the next week. After n weeks, you have 1/(2^n) of your original group who've seen you be right each week, and at your desired n, you ask for money to keep going.