Transaction value principle affirmed: imported goods valued by transaction value unless other valuation rules apply. The amendment substitutes rule 3 to make transaction value the primary basis for valuing imported goods, subject to rules 9 and 10A, and requires sequential application of rules 5-8 if transaction value cannot be determined. It also inserts four conditions into the proviso to sub rule (2) of rule 4: sale in the ordinary course under competitive conditions; absence of abnormal discounts; absence of special discounts limited to exclusive agents; and existence of objective, quantifiable data for adjustments under rule 9.