As far as I can see, a minus amount in the credit column of the journal entry, is converted to a plus amount on the debet side of the account, which is correct.
What is going on? Do you still have a balance in your accounts receivable that you want to write off against the shipping charges?
Then you better change the journal entry to:
Accounts receivable-Cash Sales 0.70 Credit, so plus amount in credit column.
And Shipping Beared by Us 0.70 Debit, so plus amount in debit column.
What you did was something like -1 (minus amount) x -1 (credit column) = +1 (amount in debet column).