1. Keep both originals
Save the written price source and the invoice as separate originals. Record the supplier, document date, currency, file fingerprint and exact row or page for each item. If the quote has changed, use the revision effective for the invoice period.
2. Align the item before calculating
Match an order reference or SKU exactly when possible. Compare pack size and unit of measure before treating two descriptions as the same item. A similar description by itself should go to human review.
3. Show the arithmetic
For an agreed unit price of USD 12.00 and an invoice unit price of USD 15.00 across 12 units, the potential price variance is USD 36.00. Show both unit prices, the 12-unit quantity, the formula and the source row for each value. Record an unmatched surcharge separately rather than folding it into that price calculation.
4. Label the state
“Potential” means the difference was identified. “Disputed” means a human approved a supplier query. “Promised” means the supplier indicated a future adjustment. None of those labels means a credit was received. Keep the currency on every amount, and do not sum different currencies without an explicit rate source and instruction.
If either document is scanned or its columns cannot be confirmed, stop the automated comparison and review it manually. A guessed row is weaker evidence than an explicit unsupported result.
See the fictional comparison