There is no default password for that version of firmware - when reset to defaults the camera is in an 'Inactive' state where you must create a new, strong, password.
If you don't see 'Inactive' in SADP, or the 'Create password' dialogue via the browser, It sounds like the seller has created a password and not advised you of it.
For similar situations, there have been posts where these have been tried with some success:
12345, 123456789abc, 123456789a both lower and upper case.