And they do exactly what you'd expect someone who has a money making machine to do- shut up and at some point kick out your external investors.
Outside finance, but similar business is sports betting syndicates. They can make 30-70% yearly return with low volatility. If you bet in 100 events per week and the expected return from each bet is just 0.5% (after expenses) you make consistent 30% return with very low volatility. If you make 1% per week you get almost 70%.
That's great return for the investment but the size of investment is typically limited to tens of millions. Brokers don't like it and close accounts when they notice them. There is increasing amount of work involved when the amount of money increases.
Can you source this? If it was that easy to get a consistent 50% return then why aren't more people doing it?
Example. If the probability of outcome is exactly 50-50, he odds they give are 1.9 and 2.11 and they pocket the difference (completely fair odds without margin would be 2.0 both sides) It does not matter what the outcome is. If they balance the bets for and against perfectly, there is no risk. They generally try to balance their liability but having preferred winner can increase profits with some additional risk.
If people place bets on the other side more, bookmakers move the odds to balance the bets from both sides. At some point the odds can be skewed so much that professional better can make money even after the bookmaker takes his margin. That money is taken from other betters. But if the bookmaker is not fully balanced it can come from the bookmakers pocket.
Maybe Ed Thorp too:
PS: If you have 1 billion to invest, call me ;)
It's always easy to see how you could have made money with hindsight. I bet if you implemented the Betting-Against-Beta and Quality-Minus-Junk strategies now you wouldn't do nearly so well.