The core question a promotion has to answer
A promotion is only worth running if it drives incremental profit — sales that wouldn't have happened at full price — that more than offsets the margin given up on sales that would have happened anyway. A discount that mostly reaches people who were going to buy regardless just hands away margin for free.
Common promotion types on marketplaces
- Coupons (a visible discount badge on the listing) — driven by shopper-initiated clipping, generally lower cost to run than a paid deal placement.
- Marketplace deal events (lightning deals, deal-of-the-day, seasonal event placements) — typically require meeting a minimum discount threshold and often carry a placement fee, in exchange for prominent visibility.
- Bundle discounts — a lower effective per-unit price for buying a multi-pack or bundle, which can increase average order value even as unit margin dips slightly.
- BOGO (buy one, get one) — effectively a 50% discount on the second unit; useful for moving inventory or increasing units-per-order, but easy to underestimate the true margin cost of.
- Site-wide or storefront-wide sales (more relevant on your own DTC site or a marketplace storefront feature) — broad discounts tied to a calendar event.
Worked example: does this discount actually pay for itself?
A product sells at $30 with a $12 contribution margin (before ad spend) per unit at full price — a 40% contribution margin. You're considering a 20% discount ($24 price) for a deal event that also carries a $150 flat placement fee.
At $24, contribution margin drops to $6 per unit (assuming the same underlying costs). To simply match the profit you'd have made selling the same number of units at full price, plus recoup the $150 fee, you need meaningfully more incremental volume than 1:1 — as a rough check: profit at full price for N units = $12N; profit at the discounted price for N′ units = $6N′ − $150. Setting these equal and solving shows you need roughly double the unit volume just to match full-price profit, before the discount has generated any additional profit at all.
This is the calculation sellers skip — a deal event that "moved a lot of units" can still have generated less total profit than doing nothing, once the fee and the margin given up on every unit (including the ones that would have sold anyway) are counted.
Questions to ask before running a promotion
- Would a meaningful share of this volume have happened anyway at full price? If yes, the discount is largely cannibalizing full-margin sales rather than creating incremental ones.
- Is there a real event-visibility boost, or is the discount simply lowering the price with no additional exposure — in which case a coupon alone (cheaper, no placement fee) may achieve the same volume more efficiently.
- What happens after the promotion ends? A large price swing can affect the price history a repricer or algorithm has learned, and can set a customer expectation for the lower price.
- Does the math work at your worst-case incremental-volume estimate, not just an optimistic one?
When promotions make the most sense
- Clearing aged or excess inventory where the alternative is a write-off or long-term storage fees — here, even a thin or negative unit margin can beat the alternative.
- Launching a new listing that needs an initial review/sales-velocity boost, where the promotion is really an investment in future organic ranking rather than a standalone profit event.
- A genuinely high-visibility placement (a major seasonal deal event) where the exposure reaches shoppers who wouldn't have found the listing otherwise.
Mistakes
- Running a discount without calculating the incremental volume needed to break even on the promotion, and just watching unit sales go up as if that alone means it worked.
- Discounting a SKU that was already thin-margin before the promotion, pushing it to zero or negative contribution.
- Repeating the same discount so often that it becomes the expected price, eroding full-price sales permanently.
Checklist
- Calculated contribution margin at both full price and discounted price.
- Estimated the incremental volume needed to at least match full-price profit, including any placement fee.
- Considered whether a cheaper mechanism (coupon vs. paid deal placement) achieves the same goal.
- Decided in advance how long the promotion runs and what happens to price afterward.