Transaction value governs customs valuation, with specified cost inclusions and Board power to fix tariff values for goods. Substitution of section 14 sets transaction value as the primary basis for customs valuation of imports and exports-price actually paid or payable where buyer and seller are unrelated and price is sole consideration-requiring inclusion of specified costs and services for imports and calculation with reference to the rate of exchange when the bill of entry or shipping bill is presented; the Board may notify fixed tariff values for classes of goods, and rules may govern relatedness, valuation where no sale or non-arm's-length transactions occur, and procedures for acceptance or rejection of declared values.