Rejection of declared value: customs may require evidence and reject value when reasonable doubt persists after enquiry. The proper officer may require further information and, if reasonable doubt about the truth or accuracy of a declared value remains after enquiry or absence of response, may deem the transaction value indeterminable and reject the declared value; the importer can request written reasons and a reasonable opportunity to be heard prior to final rejection. Where rejected, value determination proceeds sequentially under subsequent valuation rules. Grounds for doubt include significantly different assessed values for comparable imports, abnormal or exclusive discounts, misdeclaration or non declaration of material parameters, and fraudulent or manipulated documents.