There's one for you, nineteen for me
They may not be taxed on point of impact. eg I know in America, jackpots over a certain level are taxed, but there is still an obligation to report gaming winnings in other countries & volunteer tax if gaming is your primary income.
Where it gets interesting: If Mr. Martingale & Mr. Shrewd buys shares, the former loses & the latter wins, they may post their respective loss & win at the end of the financial year, as the tax dept. readily accepts they were engaged in a business activity, ie both were involved in trying to make a profit.
Now if this pair turn up at the casino, & Mr.Martingale loses his shirt following a system of his own namesake, & Mr. Shrewd wins using a better system, the taxman won't acknowledge Mr.Martingale's loss, but is happy to take a piece of Mr.Shrewd's action.
Think about it. Both men went to the casino & followed a system. If the winner has tax liability, why doesn't the loser have a legitimate claim for his loss. Who's to say how much the winner won anyway, or even if that can be established, his other losses?
I don't know any pro's who pay tax, & I don't know any who have been prosecuted. I believe a prosecution could lead the way to a fight in the higher courts which the Gov't would not want to entertain, ie some radical judge who's about to retire, will allow the Gov't to enforce their tax on the miniscule no. of pros, & rule in favour of losers claiming their losses. Don't think it can't happen. Years ago a higher court in my land ruled that people could claim monetary costs against the police where police lost the case. The Gov't got it ovveruled, but not before many months & many millions of dollars were expended.
What I do believe is that if you claim unemployment benefits & it can be shown you're living the life of Riley, fraud charges could be laid against you. Besides this is pretty f*&^ed, if you're a pro you should have more productive things to do than wait in queues & turn up at job interviews. If you're struggling, maybe.
Mr Shrewd would be wise to have other assets such as property & pay the tax on his profits, so as to make a societal contributon, charities could use a little help also if you feel guilty.
I would be interested in hearing other, perhaps more learned opinions. I went to an accountant & he stated if I volunteered tax as a pro gambler I would probably get audited!
Luckily I don't have to worry as my wife & I earned a high income for many years prior to gambling, so we can legitimise our assets. We no longer live on baked beans & pay off the mortgage with the money we stuffed into our mattress over the last ten years. "The truth, Your Honour, may I be struck by lightning if a lie ever passed these lips."