Although the casino can detected that, those gamblers will not stop for trying to do the same thing. Maybe they will try in the other casinos that they don't use before so they think that they will have the chance to pass the blocked.
But the casino smarter than we think because casino have a team that can check and identify those abuse that happen in their place. If they found their members sell their account to other people, they will not tolerate it and will ban the connection from that people.
It is never ending story between the casino and the gamblers so it will still continue. We don't have to be like them and it is better we use gambling for fun only.
Some gamblers do it without the casino finding out, it is only few people that do not use their head when they have already been caught before that they catch again. After buying casino account and they use it under covered without revealing that they are not the owners of the information that was used to complete the kyc, It is when they want to withdraw that they make a mistake by trying to withdraw a large amount instead of withdrawing in smaller values that will not raise attention to their transactions. Nobody is going to ask you to verify your identity when you withdraw $500 to $1000 but when you withdraw amount like $5000 and above, it can get to the attention of the casino or when you withdraw multiple times in a row or in a day.