Sales of books were made each year by the taxpayer to a distributor. The taxpayer was obliged to repurchase any books which the distributor might elect to return. The taxpayer at the end of each year was not entitled to deduct a reserve in respect of estimated returns. "[T]here had not been any history of uncollectable accounts between the Appellant and the [distributor]. Thus, historically, there was no reason or basis for setting up a reserve for bad debts, nor in fact, was such a reserve ever set up."