Separate customer price from campaign cost
A product supplied without a separate charge still comes from inventory. Quantity and the agreed costing approach matter to campaign assessment, not only the sales document price.
Use the same calculation scope across comparisons. Including additional handling in one campaign and only product cost in another does not produce an equivalent comparison.
Connect the issue with the promotion
Record why the product was supplied and which condition it fulfilled. A warehouse movement alone does not distinguish a campaign benefit, a product for an agreed test or another issue reason.
Check quantity against the rule too. An extra product per order differs from one awarded after a purchasing level is reached.
Assess cost alongside the objective
Higher turnover alone does not establish that free goods were worthwhile. The assessment needs the goal, data scope and other commercial conditions.
This is especially useful to finance teams. Trade Marketing retains campaign context while WMS records the actual issue. Connecting them reveals a cost that cannot be understood from the customer's payment alone.