a firm does not willingly sell at below selling price but it uses marginal costing to assess whether to accept an order for below selling price or not. if the price is above variable cost per unit, the revenue can contribute to fixed costs. the fixed costs need to be paid even if there is no production which is why the firm may accept orders at below selling price so as to lower the losses. i guess!then the firm will not sell below the selling price. if it could make a profit on selling price then why charge a low price. never mind, that question was confusing