Who is this user and what actually happened? I believe we should hear his/her side of the issue. That situation might be something to learn from if our accounts, despite being innocent, might have the same issue. Can you post the links of his posts?
There are many such cases. Let me just list the 3 recent ones, and all have been resolved in favour of those accusing the casino.
1.
https://bitcointalk.org/index.php?topic=55287562.
https://bitcointalk.org/index.php?topic=55353353.
https://bitcointalk.org/index.php?topic=5530971Do you believe that they are merely guessing?
I think they are, or their flagging system has a lot of false positives. Reason being, after telling the user to list all his other accounts, they eventually unlock the blocked account if the user insists over several days or weeks
He/she should also ask them HOW they made the absolute conclusion that he/she has more than one account.
Those are the methods casinos don't disclose, but at least they should be able to list to the user the accounts that are linked to his instead of asking him to list them.
A user in Shuffle's topic posted that the root of the problem for such issues when the casino asks you for your "other accounts" was probably because there more than one user in the same household/using the same I.P. Address. That probably turned on a sort of "alarm" in their system, telling them that users are playing with more than one accounts.
Although the resolution will be a case to case basis, depending on those accounts' playing patterns. But it is also possible that one person is playing under different accounts using his/her wife's/husband's/sister's/brother's information.