So, Do you also think this is true?
Even today, there are still many people who practice black magic and dark arts. I don't know actually how it works and haven't witness any so I don't know how true it is.
I only have read or watched a related example on Harry Potter. When Harry let Ron drunk the potion he had won in their potions class (forgot the name though) to let Ron perform well in their quidditch match. It's not actually gambling, but it's the only reference I remembered. Lol!