Rejection of declared value: procedural grounds allow tax officers to reject supplier valuations and determine value sequentially. When a tax officer has reasonable doubt about a supplier's declared transaction value, the officer may require further information and, if doubts persist or no response is furnished, treat the transaction value as not determinable under the primary valuation provision. Grounds for doubt include significant variance with comparable transaction values, divergence from contemporaneous market value for like goods or services, and mis-declaration of description, quality, quantity, or year of manufacture. The officer must notify the supplier in writing, provide a reasonable opportunity to be heard, record reasons if unsatisfied, and then apply alternative valuation methods sequentially.