Rejection of declared value allows customs to question and set aside invoice value where reasonable doubt exists, with procedural safeguards. Rule 10A authorises the proper officer to reject a declared transaction value when there is reason to doubt its truth or accuracy; the officer may seek further information and, if doubt persists, the value is treated as not determinable under the transaction value provisions. On request the officer must state grounds for doubt in writing and provide a reasonable opportunity to be heard before a final decision is taken.