| Totals wrong, or a client-sent total is trusted | Recompute every component server-side from stored data; reject on mismatch (Rule 1) | payments.md |
| Charged twice, webhook replayed, or events arrive out of order | Idempotency key from the order id + dedupe on the provider's event id (Rule 2) | payments.md |
| Paid in the processor, missing in the store | Daily reconciliation of processor charges against orders, by date range | payments.md |
| Declines rising, 3DS/SCA failures, or a retry loop | Hard vs soft decline codes, exemption routing, capped re-attempts | payments.md |
| Payout does not match revenue | Rebuild it: gross − refunds − disputes − fees − reserve ± FX | payments.md |
| Carts abandon at a specific step | Instrument the funnel step by step; the field that fails names the fix | checkout.md |
| Abandoned-cart recovery, express pay, guest checkout | The 1h/24h/72h ladder, wallet placement, address validation | checkout.md |
| Oversold across channels | One source of truth, buffer formula, sync interval by SKU velocity (Rule 3) | inventory.md |
| Stockouts, dead stock, or cash trapped in inventory | Reorder point, safety stock, turns, ABC classing | inventory.md |
| Variants, SKUs, GTINs, bundles, digital goods, product copy | Model the attribute once; feeds, filters and marketplaces all read it | catalog.md |
| Carrier choice, rate tables, packaging, 3PL vs self-ship | Zone/weight band math, cost per order, the 3PL break-even | fulfillment.md |
| Parcel lost, late, damaged, or delivery disputed | Exception ladder, who pays, when to reship without asking | fulfillment.md |
| Returns, refunds, exchanges, restocking, return abuse | Windows, inspection, partial-refund grid, per-customer thresholds | returns.md |
| Orders stuck, split, edited, cancelled, or duplicated | State machine, stuck-order alerts, partial shipment and edit rules | orders.md |
| Angry customer, SLA target, or what to compensate | Response targets, escalation triggers, compensation ladder | support.md |
| Chargebacks, fraud screening, account takeover, promo abuse | Score thresholds, liability shift, the representment evidence pack | fraud.md |
| A discount, bundle, promo, or price change | Contribution-margin gate and the discount ceiling (Rule 4) | pricing.md |
| Conversion work, product page, trust, A/B test | Prioritization, trust elements, sample-size math (Rule 7) | conversion.md |
| Repeat purchase, LTV, loyalty, win-back, reviews | Flow ladder, cohort reading, RFM segments | retention.md |
| Subscription revenue, churn, dunning, pause/skip | Churn math, the dunning ladder, prepaid vs month-to-month | subscriptions.md |
| Ad spend, product feeds, store SEO, channel mix | Payback gate, break-even ROAS, feed hygiene, PDP/category SEO | acquisition.md |
| Amazon/eBay/Etsy, buy box, channel conflict | Fee-stack math, listing economics, facilitator tax | marketplaces.md |
| Choosing a platform, replatforming, going headless | TCO formula, migration order, the redirect map | platforms.md |
| Slow store, weak site search, images, accessibility | CWV targets, faceting rules, image pipeline, a11y floor | storefront.md |
| Two tools report different numbers | One definition per metric, tracking plan, consent and server-side tagging | analytics.md |
| VAT/OSS, sales-tax nexus, invoices, consumer law | Registration triggers, filing calendar, mandatory disclosures | tax.md |
| Black Friday or any peak window | Freeze window, load, stock cover, staffing, budget pacing | peak.md |
| Wholesale, net terms, price lists, MOQ | Tier design, credit exposure, tax exemption, channel conflict | b2b.md |
| Anything else ecommerce | Answer directly, then name the contribution margin it moves and the metric that will show it | — |