Callie is right.
You do need a reciept or have used a credit/debit card to pay. They can look that up.
If you paid check or cash, without a reciept, you will have to ask for a manager and if you are really sweet, talk highly of the brand they will most likely override. Keep your eye out for a helpful salesperson and they will do their best to help you. Act like you really need their assistance and they happily take care of you. Act like you may want an Old Navy Store Credit Card and they'll be your best friend
However, if it looks like an even exchange is not going to happen, please do not freak, but be prepared to be issued a "refund check". Under quite a few circumstances if you are do not have reciept and are not eligible for balance to be put on gift card, then the cashier is required to get your driver's license and mailing info. You will recieve your refund in the form of a check payable to you that you can then deposit/cash at your bank.
It is hard to believe that this is a chain store's policy in todays world but I have seen it happen.
Keeping reciepts are so important.
One tip given to me was to use one of those small accordian coupon holder and keep reciepts in there under categories and then after a few months move them into permanent files.
Good luck and keep us posted how it turns out.
P.S. Don't get me started on their shoplifting policy (or should I say lack of action). It blows my mind.
