How to handle a return

[Jeyamaran]

Hi,

I have some customers who has returned their items and I issued a refund for them. Then I used the credit memo to show this in QB. But it shows a negative balance(it should be $0) in the customer report. Eventhough I have reconcilled my bank accounts, I can never get rid of this negative balance.
So, What I am worried about is, If that customer buy something in the future, will this negative balance get adjusted for the new purchase?(which would be terribly wrong)?
How do I fix this? Please help me.
Thanks