Transaction defect
A seller-initiated out-of-stock cancellation counts as a transaction defect under widely reported eBay policy.
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Decionis for Commerce
Answer · Stop overselling across channels
How do I stop overselling the same item across Shopify and eBay?
To stop overselling the same item across Shopify and eBay, validate live inventory at the millisecond of checkout and halt the double-sale before the order commits. Decionis checks the real, current stock state at the moment the checkout token is issued — in under 120ms of decision compute — and holds any order that would sell inventory already committed on another channel, sealing the decision into an Ed25519-signed Decision Dossier. It is deterministic, not an AI forecast, and installs read-only in Shadow Mode first, so you see every oversell it would have caught across channels before it enforces a single hold.
Why overselling costs more than the lost sale
The real penalty is your seller standing. These are widely reported eBay policy thresholds, not Decionis-measured stats — but they are exactly what a double-sale cancellation puts at risk.
< 0.5% defects
Top Rated Sellers must keep their transaction defect rate below 0.5% — a few oversells can breach it.
≈ +6% fees
Falling to Below Standard status is widely reported to add roughly 6% to final-value fees on top of the lost sale.
The verdicts
One certified outcome per order — deterministic from the live inventory state every time.
Allow
Live inventory confirms the unit is available and uncommitted — the order commits, recorded as a signed pass.
Hold (block)
The unit is already committed on another channel — the double-sale is halted before the order commits.
Review
Inventory state is stale or unreadable at the moment of checkout — flagged rather than guessed. Never a fabricated stock count.
What the Decision Dossier records
Every halted or allowed order produces a signed, exportable receipt — the proof you held the double-sale, defensible if a channel disputes the cancellation.
| SKU / variant | The item evaluated at the checkout boundary |
| Channel | Where the order originated — Shopify or eBay |
| Live on-hand | Real, current stock state read at the millisecond of checkout, never assumed |
| Committed elsewhere | Units already reserved or sold on the other channel |
| Available to commit | On-hand minus commitments — the deterministic verdict input |
| Verdict | Allow, hold, or review — one certified outcome at the order boundary |
| Policy version | The encoded inventory-truth policy and rule digest that governed the decision |
| Signature + hash | Ed25519 signature over the canonical SHA-256 of the dossier (when the prod key is provisioned) |
It governs inventory truth, never your operations
- How much stock to buy or how to allocate it across channels — that is your operations decision.
- Demand forecasting — Decionis validates the live state at checkout, it does not predict future stock.
- eBay listing quality or shipping performance — those are separate seller-standard inputs.
- An end-to-end checkout latency claim — only the deterministic policy evaluation is benchmarked at <120ms; the platform runtime and network are outside Decionis's control.
Frequently asked questions
Stopping cross-channel overselling, and protecting Top Rated Seller status.
How do I stop overselling the same item across Shopify and eBay?
Validate live inventory at the millisecond of checkout and halt the double-sale before the order commits. Decionis checks the real, current stock state at the moment the checkout token is issued — in under 120ms of decision compute — and holds any order that would sell inventory already committed on another channel. The check is deterministic, not an AI forecast, and each halt is sealed into an Ed25519-signed Decision Dossier.
How does overselling threaten my eBay Top Rated Seller status?
As widely reported in eBay's seller policy, a seller-initiated out-of-stock cancellation counts as a transaction defect. Top Rated Sellers must keep their transaction defect rate under 0.5%, so even a handful of oversell cancellations can cost the status. Falling to Below Standard is widely reported to add roughly 6% to final-value fees — an economic penalty layered on top of the lost sale.
Is this an AI inventory forecast?
No. Decionis is deterministic — it validates the live stock state at the exact moment of checkout, not a probabilistic prediction of future availability. The same inventory state and the same order always produce the same verdict, with no model drift.
Do I have to enforce holds right away?
No. Decionis installs read-only in Shadow Mode first. It observes real checkouts across Shopify and eBay and records every double-sale it would have halted, so you can see the oversell exposure before you enable a single enforcement hold.
Self-serve · read-only first
Watch it halt a double-sale — before it costs you a defect.
Run a cross-channel order through the sandbox, read the signed Decision Dossier showing the live inventory state, then enable enforcement from the quickstart when you're ready.