Hello @aciceri and well done, you spot a problem 
Honestly, it’s not the only one 
people could also use AI to bet on the right answers and win easily.
Is there a solution? Probably some solutions can cover particular aspects but not all. For example in your case, a mitigation could be a mechanism of staking for quiz creators or a reputational rate for good actors.
In professional online assessments, some platforms use the camera and the mic to catch eye-tracking, key clicks, background voices, etc. It is an automatic quality check where an auditor is triggered by alarms and manually validates specific video frames recorded.
I don’t want to go on that route at this stage, I want it simple and focused on the main concept. Perhaps this version can be just for fun where students play with tokens with no values and a future version (for academic degree purposes) uses tokens with real value but with anti-cheating mechanisms.
Thank you for your intelligent comment which allowed me to clarify an important aspect of the proposal.
Cheers,
Mario