Check what the number means
A customs unit value is typically a reported value divided by a quantity or weight. It is not necessarily an offer, an invoice price for a comparable grade or a current market quotation.
Align the measures
Use the same currency and denominator. For a weighted average, divide total comparable value by total comparable weight; do not simply average record-level prices.
Match basis, grade and period
Separate FOB from CIF where known. Compare similar product descriptions, grades and periods. Freight, concentration and product mix can explain part of an apparent gap.
Keep missing data visible
If the source does not report a value or valuation basis, do not manufacture one. Use the measures the source supports and explain the limitation.