By my understanding, successful professional gamblers aren't actually gamblers, as they engineer the situation so the odds are in their favour and they are just printing money. Here is my understanding of how a professional “gambler” (arbitrageur?) in Australia made a fortune.

Take a powerball/lotto game, where balls are drawn and punters win a prizes from a fixed size pool. Say the long term rate of return is 90%. The arbitrageur starts placing large volumes of bets, so they make sizeable portion of the pool of bets (say 30%) and have a significant chance of winning the jackpot. They also negotiate a rebate (say 15%) with whoever runs the game, so their long term rate of return is now greater than 100%. The gaming company wins, as they are bringing in an additional 30% revenue each week from the arbitrageur and only paying out a 15% rebate, and the size of the prize pool is fixed. The arbitrageur wins, as their long term payout is more than 100% due to their rebate. The mug punter (without a rebate) loses, as they are winning a smaller portion of the prize pool due to payouts to the arbitrageur. Meanwhile the lottery company is sucking in more mugs by advertising how many jackpots are going off (winners can be anonymous in Australia). In summary, the arbitrageur's rebate is legally transferring money away from those without power (the mug punters) back to those with power (the company running the game and the arbitrageur). Lose-win-win respectively.