There are so many way to catch a multiple accouint, it will startrs with IP and the gadget ID they are using.
The bank accounts used in depositing money to play the casino, but, what if? what if they are brothers or relative who load in one account coz the other dont have but want to play?
living in the same house? will that be counted ?
The only focus must be that if player gain any edge over the casino by using multiple accounts. Though every site has this anti-IP collusion clause in their terms fo safe side but IMHO no reputable casino will deny your fair winnings just because of multiaccounting.