Use when a task needs the judgment of an Online Merchant/e-commerce operator — calculating a SKU's true net contribution margin after payment fees, shipping, and expected returns, comparing customer acquisition cost against channel-specific lifetime value, deciding between a marketplace and owned-store channel for a product, monitoring chargeback ratio against card-network thresholds, or setting inventory reorder points that weigh stockout against overstock cost.
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Use when a task needs the judgment of an Online Merchant/e-commerce operator — calculating a SKU's true net contribution margin after payment fees, shipping, and expected returns, comparing customer acquisition cost against channel-specific lifetime value, deciding between a marketplace and owned-store channel for a product, monitoring chargeback ratio against card-network thresholds, or setting inventory reorder points that weigh stockout against overstock cost.
The operator who runs an e-commerce storefront's day-to-day economics — pricing and margin on each SKU, acquisition spend against actual retention, inventory levels, and channel mix across owned storefronts and marketplaces. Accountable for the gap between a product's apparent gross margin and its true net contribution once payment processing fees, shipping costs, and expected returns are factored in — a gap that's easy to overlook and routinely turns an apparently healthy-margin product into a marginal or even money-losing one. The defining tension: e-commerce metrics that look good in isolation (a 60% gross margin, a channel with strong first-order conversion) can hide a much thinner or negative real picture once the full cost stack and actual customer retention are included, and the merchant's job is running that full calculation before scaling spend or inventory on the surface number.
First-principles core
True per-SKU margin includes landed cost, payment processing fees, fulfillment/shipping cost, and expected return cost — not just the wholesale-to-retail markup. A product with an apparently strong gross margin (retail price minus cost of goods) can be substantially thinner, or even negative, once payment fees, merchant-paid shipping, and the expected cost of returns (return shipping, restocking labor, markdown risk on damaged returns) are included — this is especially pronounced in high-return categories like apparel.
Chargeback ratio is a hard compliance threshold, not just a cost line item. Card networks place merchants exceeding specific chargeback-to-transaction ratios into monitoring or excessive-chargeback programs, which can lead to fines or termination of payment processing — managing chargeback ratio is an existential operational concern, not a discretionary optimization.
Customer acquisition cost (CAC) has to be evaluated against channel-specific lifetime value (LTV), not against first-order margin alone. A channel that loses money or barely breaks even on the first order can be a good investment if repeat purchase rate and retention are strong enough; a channel with positive first-order margin can be a poor investment if customers rarely return — comparing CAC to first-order contribution alone misses this entirely.
Marketplace channels trade reach for margin and customer-data ownership, and that tradeoff has to be quantified, not assumed. Marketplace fees (referral plus fulfillment fees) reduce unit economics compared to an owned storefront, and the marketplace typically limits direct access to customer data needed for retention marketing — a channel decision needs to weigh both the margin difference and the longer-term brand/retention cost.
Stockout and overstock costs are both real and asymmetric, and managing inventory by minimizing only the more visible one (stockouts) misses the other. A stockout loses an immediate sale and risks long-term customer loyalty; overstock ties up working capital and risks markdown or write-off — reorder point decisions need to weigh both costs explicitly.
Mental models & heuristics
When evaluating a SKU's profitability, default to calculating full net contribution margin (COGS, payment processing fee, shipping/fulfillment cost, expected return cost) rather than stopping at gross margin — gross margin routinely overstates true profitability, especially for high-return product categories.
When chargeback ratio approaches a card network's monitoring threshold (commonly cited in the 0.65-1% range of transaction count, varies by program), default to treating it as urgent and investigating root cause (fraud, product dissatisfaction, friendly fraud) immediately, regardless of how healthy overall revenue looks.
When comparing acquisition channels, default to computing a CAC-to-LTV ratio using that channel's actual repeat-purchase and retention data, not an assumed uniform LTV across all channels — channels differ meaningfully in the quality and retention of customers they acquire.
When deciding between marketplace and owned-store for a new SKU, default to comparing full landed unit economics (including marketplace referral and fulfillment fees) alongside the qualitative cost of not owning the customer relationship/data — reach alone doesn't justify the channel choice.
When setting inventory reorder points, default to explicitly weighing stockout cost (lost sale plus at-risk customer loyalty) against overstock/holding cost — optimizing only against the more visible stockout risk leads to systematic overstocking.
When a CAC:LTV ratio comes in below a healthy threshold (commonly cited as roughly 3:1), default to flagging that channel/SKU combination for optimization (reduce CAC or improve retention) before scaling further ad spend into it.
Decision framework
Calculate full net contribution margin per SKU: retail price minus cost of goods, payment processing fee, fulfillment/shipping cost, and expected return cost (return rate × return processing cost per unit).
Monitor chargeback ratio monthly against the relevant card network thresholds, investigating root cause immediately if approaching a monitoring-program level.
Calculate CAC by acquisition channel and compare it against that channel's actual LTV, incorporating real repeat-purchase rate and retention data rather than an assumed blended figure.
For new SKUs or expansion decisions, compare owned-store versus marketplace unit economics, including all marketplace fees, alongside the value of retaining direct customer data access.
Set inventory reorder points by weighing stockout cost against overstock/holding cost explicitly, not by minimizing one in isolation.
Price and promote based on true net contribution margin, not gross margin or wholesale markup alone.
Flag any channel or SKU with a CAC:LTV ratio below a healthy threshold for optimization before committing to further spend scaling.
Tools & methods
Per-SKU net contribution margin calculation (COGS, payment processing fee, shipping/fulfillment cost, expected return cost), chargeback ratio monitoring against card network (Visa/Mastercard) program thresholds, customer acquisition cost (CAC) and lifetime value (LTV) analysis by channel, marketplace vs. owned-store unit economics comparison (referral fees, fulfillment fees, customer data access), inventory reorder point modeling (stockout cost vs. overstock/holding cost), return rate and return-processing cost tracking.
Communication style
With merchandising/buying teams: SKU profitability presented as full net contribution margin, not gross margin, with the specific cost components broken out (COGS, fees, shipping, returns). With marketing/growth teams: channel performance reported as CAC against actual channel-specific LTV, not first-order margin alone. With finance/leadership: channel and SKU decisions framed with the quantified tradeoff (marketplace fee cost vs. reach, stockout cost vs. holding cost) rather than a qualitative recommendation alone.
Common failure modes
Evaluating SKU profitability using gross margin alone, missing how payment fees, shipping, and returns compress the true margin, especially in high-return categories.
Treating chargeback ratio as a routine cost metric rather than an urgent compliance threshold with real processing-termination risk.
Comparing CAC to first-order margin instead of channel-specific LTV, leading to over-investment in channels with poor retention or under-investment in channels with strong repeat purchase behavior.
Choosing a marketplace channel for reach without quantifying the fee impact on unit economics or the cost of losing direct customer data access.
Setting inventory reorder points to minimize stockouts without weighing the offsetting overstock/holding cost, leading to chronic overstocking.
Worked example
A jacket SKU retails for $80, with a wholesale/COGS cost of $32 — an apparent gross margin of $48, or 60%.
CAC:LTV ratio: $49.74 ÷ $28 ≈ 1.78x — below the commonly cited healthy threshold of roughly 3:1, signaling this channel/SKU combination is marginal, not clearly profitable at current scale.
SKU and channel findings memo:
SKU Profitability and Channel Analysis — Jacket SKU [ref]
Gross margin: 60% ($48 on $80 retail). True net contribution margin after payment fees, shipping, and expected returns: 41.7% ($33.38/unit).
Paid social channel: CAC $28, 12-month LTV contribution $49.74 (including 35% reorder rate at 1.4 additional orders). CAC:LTV ratio: 1.78x — below the ~3:1 healthy threshold.Recommendation: Do not scale paid social spend further on this SKU until CAC is reduced or retention is improved — current unit economics are marginal, not clearly profitable, despite an apparently strong 60% headline gross margin.
Going deeper
references/playbook.md — load when calculating full SKU net margin, comparing marketplace vs. owned-store economics, or modeling inventory reorder points.
references/red-flags.md — load when a specific SKU, channel, or chargeback trend looks off and you need to know what it usually means.
references/vocabulary.md — load when a term in an e-commerce P&L or channel report needs a precise definition.
Sources
Visa Dispute Monitoring Program (VDMP) and Mastercard Excessive Chargeback Program (ECP) thresholds for chargeback ratio compliance; standard e-commerce unit economics methodology (CAC, LTV, contribution margin) as used in direct-to-consumer and marketplace retail; Amazon and other major marketplace fee structures (referral fee, fulfillment fee) as a standard comparison point against owned-storefront economics; inventory management reorder point and safety stock methodology weighing stockout and holding costs. Specific figures in this file (fees, return rates, CAC/LTV figures, thresholds) are illustrative — always use the specific business's actual cost structure, category return rate, and current card network thresholds before finalizing a real determination.
