That can happens to gamblers where they will still playing gambling without paying tax if they win because they know how to hide their winning. Tax should be impose but the officers who does their job must be clear from any illegal things so the tax can be distribute to the right place.
What if the government makes casinos act as withholding tax agents? Winning gamblers wouldn’t be able to evade their tax liability. This could likely happen if the government notices a gap between tax collection and their expectations. They’d have the data from gambling sites, which are required to report it, so they’d know exactly where to step in.