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.
No casinos will just nail two accounts if those accounts haven't committed any crime against the casino in the first place, and most casinos will get and connect accounts that have proven cases of accounts abusing their casinos with may be taking part in promotions and bonuses or using same to refer each and taking their percentage income, this is when a casino could treat multiple accounts abuse, but if an account is a Link to same IP and without violating any of the casino's rules I don't think it will be a big deal having such case, so if you share same IP with someone else it doesn't automatically translate into violation of rule until the crime itself is committed.