A discount can lift sales quickly, but sales alone do not prove that a campaign created value. Customers may buy earlier, switch from another product in the category, or appear only when an offer is available. Looking only at campaign revenue can lead a team to repeat a mechanism that erodes gross margin.
Separate incremental demand from shifted demand
Compare promotion sales with a credible baseline: comparable weeks, a seasonally adjusted prior-year period, or a group that did not receive the offer. The difference is the candidate for incremental sales. Then examine related products. A strong offer on line A can move customers away from line B, where margin is higher. Each added order must also be assessed alongside the discount, delivery, gifts, fulfillment, and communication spend.
Follow behavior after the offer
Set a 30-, 60-, or 90-day review point that fits the purchase cycle. Check whether customers return, whether later orders still need a discount, and whether they move into other products. Every campaign also needs a stop rule: incremental sales no longer offset lost gross profit, new-customer share is below target, or substitute-product sales fall too sharply. Before approval, identify the behavior to change, the measure that proves the change, and the loss that is acceptable in exchange.
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