This is not applicable because as soon as the person logs into the account from the restricted area, the casino would capture the IP address which would reveal where he's gambling from and the account would be flagged.
Are you from country that gambling is restricted and know that no one from the restricted location are buying gambling site account? It is very possible for someone in a restricted country to do that. Sooner or later, the person might be known and verification can be requested for again by the gambling site. But do you know that some people are paying for such and get verification again from the seller? There is a reason many sites start adding live video to their verification.
You posted what is happening in reality as false.
Casinos have tightened their rule, if he deposits very substantial amounts, he might be asked for additional documents and proof of funds which he cannot provide and would forfeit the funds.
The only way this is applicable is if there's a corrupt casino inside man that would facilitate the laundering while they legalize the funds by passing it through the casino.
But still that does not make it impossible for money laundering. You have not seeing laundering cases that the launderers will not be traced because of this, but tracing it to another person's identity.
At least, the OP will use this to know they selling his gambling site account can be dangerous. Until it happens would be when some people will know.