To give some details, the main betting exchange I use is Betfair, a UK betting company part of the same group that own Fanduel, and I place bets for or against outcomes in the last half an hour before the start. For example, you can back a team to win meaning you make a certain amount if the team wins, but you can also lay a team, meaning that if that team doesn’t win (another team wins or it’s a draw) you win that bet, with a payout of inverse the odds. There is no crypto involved, just GBP, and Betfair is a multibillion dollar company paying taxes and subject to the law and the UK regulating bodies. I have a model to predict short term movement in the odds, which is not amazing but enough better than random that it can overcome the fees and spread between the back and lay odds and be profitable.
If you mean as a percentage of my investment, it’s about 1000%, but I can’t scale up further, so it doesn’t grow exponentially. If I increased my stake tenfold I wouldn’t be making more bets or more money. It’s like with market makers or Renaissance Technology, I’m limited by the market opportunity so the roi or sharpe ratio or whatever don’t really make sense.
Any further questions?