An easy way to do this is with their email, I know people that use the very same email for everything, which means that if at some point a hacker gets into that email then they can get all kind of information from them, but if instead they decide to use a different email for their personal matters, the different exchanges they use and the casinos in which they like to play then even if one of those emails got compromised they will lose only a limited amount of information.
Right different mails for different casino is also good option in order to be safe in case any of the account is compromised you other mails remain safe but if you have used them on multiple accounts then it's risky.But also remember which email is linked to which account in case you need them at any time.