Well, I think not all of them [I saw casinos that allow multiple accounts]--in this case, you must open to them is if you are allowed to create another account. Perhaps the possible reason is prone to abuse, running two accounts in one casino is everywhere restricted and that is always on their TOS. However, in scam accusation has a different story, but usually, cases are users did not read the TOS and without knowing them they already prohibit the law which is very risky, the most punishments is blocking your account. If you deactivated one and then create another one, there is no problem but I think always read the TOS will not put you in danger and it is best if you have one account.
Having more than one account is really prone to abuse.
This is the major reason why most casinos are not allowing such practice.
For those scam allegations, most of them haven't read the ToS of the site before creating their other accounts.
So it is not the fault of the site, but the player himself.
And if you are a gambler, what do you think is your main reason of creating another account?
Though some just want to separate their activities but a lot are after for some referral bonus or other things that the site deemed as abuse.
This topic should be moved to gambling discussion board -
https://bitcointalk.org/index.php?board=228.0.
The reason of separating activities is too weird already, why not put it all on one account? as having multiple accounts is already suspicious and the reason mostly behind making multiple accounts is to abuse the system, the freebies, the referral bonuses, if Casinos let users get away with this then that's just poor management and security overall, unfair and abusive, even if it's not the Casino's fault and the player not reading the ToS, the toll would still be on the Casino itself because they've let users spam and abuse this kind of system.
