Who are these punters ? And I suspect you will find they were not "gambling". For example, If you trade out (arb) then you are now trading stock and are not officially gambling.

There is NO chance of person who actually backs horses or sports being ever taxed by the ATO.

ALso if your talking about David Walsh and Zeljko Ranogajec and his club then they were not gambling either. They were being paid to provide liquidity which again is not gambling.

If you trade out of your positions... then yes you should be taxed. If you are just placing a bet on a horse or horses and you can lose the whole amount then the ATO will not chase you.