Suggestions:
In the system, when Sales return is done, the effective amount, which is the sum of returned and replacement value. As the replace value comes in negative the effective amount shows the difference between the value of return and replacement. If the amount is within the permissible limit system will allow you to confirm the Sales return.
There is a reverse of account for sale returns as though no sale had occurred in the first place.
Hence, the value of goods returned must be deducted from the sale revenue.
If sale was initially made on credit, the receivable recognized must be reversed by the amount of Sales returned. System debits Sales return account and credit debtors account.
If the Sales in respect of the returns were made for cash/bank, then a payable must be recognised to acknowledge the liability to reimburse the customer the amount he had paid for those Purchases. System debit Sales return account and credit cash account.