Amounts received in payment of the sales price of property held by the seller until the total amount of the sales price is paid to him are taxable in the month during which such amounts are received by the seller. In the event of the failure of the buyer to complete is payments, no refund of taxes paid on the amounts received by the seller will be made except where the seller refunds all amounts paid to him by the purchaser.
S.C. Code Regs. § 117-318.3