[shou4577]

Maybe a bit off-topic, but this scam has always intrigued me. You can, in fact, do better than just "Money back guarantee!" You can do as much as, say, "We'll give you your money back, plus an extra 50% of the fee!" So your "customers" pay $50, and if you are wrong you give them back $75. You still make $12.50 on average per customer by guessing randomly, so long as you scam sufficiently many people.

[waterside81]

This is precisely how sports handicapping services work. Every week, 50% of your customers are happy and return, the other 50% are unhappy and might not return.