If you have a cash back credit card, at some point the business will get a check. That check is an income to the business.

Create an service item called cash rebate, and point the income account to “other income” or create a rebate income account, set the item to non-taxable.

Create a customer whos name is the name of the credit card. i.e. Capital One, Advanta, etc etc

When you get the cash rebate check, bring up a sales receipt, select the customer, on the first line enter the item cash rebate, and enter the amount, then enter the type of payment as check and the check number, save it.

That puts the check in undeposited funds ready for you to deposit it, and the amount went to the income account.