Questions:
1) Do you carry over negative balance?
No we do not. ReferBack does not carryover negative balances – at the end of each month the whole game starts again!
2) Is the winning player removed from the account?
Due to the above – no!
3) The webmaster has to request a non negative carry over agreement?
As above – no!
4) Any restriction?
4 out of 4 – No again! 
Cheers,
Shane