Technical guide · real-time inventory and overselling control

Who is this guide for? Retail and technical teams whose physical POS and web store sell from the same stock.

Reliable POS and ecommerce synchronisation does not come from writing the latest balance into two systems. Every sale, return, cancellation, count and correction should be a stock movement with a source. Calculating sellable quantity from movements and reservations makes the number auditable and recoverable.

Build an inventory ledger, not a balance field

“Stock equals seven” cannot explain why it equals seven. Record receipt +10, till sale −1, web reservation −1 and count difference −1 with time, warehouse, user and source order. An incorrect event can then be reversed without silently rewriting history.

MarketOne barcode POS sales screen connected to central inventory — **A real screen from MarketOne.** Barcode sales and the online catalogue work within the same product and stock context.

Define the sellable-inventory formula

A basic model subtracts open reservations, safety stock and blocked items from physical quantity. Basket reservation duration, the moment a marketplace order becomes firm and when a store transfer becomes available must be explicit rules. Otherwise every channel interprets the same number differently.

What if the same event arrives twice?

Connectors can repeat messages or time out after a successful action. Give every stock event a durable identity so a duplicate cannot reduce quantity twice. If a channel update fails, the queue retries safely while the central movement remains single. This idempotent design is essential during promotion peaks.

Stress the model with the final unit

Scan the last unit at the till while a customer reaches payment online. Measure precedence, reservation duration, customer messaging and channel update latency. Then return the till sale and verify that the reverse movement reaches the correct warehouse and channels.

Technical tests against overselling

Model sale, return, cancellation, count, transfer and correction as separate events.
Define expiry and release rules for basket and order reservations.
Prove that a duplicate message cannot change stock twice.
Record queue, retry and alert behaviour during channel failure.
Make every balance traceable to its source movements.

Example stock events

Event	Central effect	Channel result
Till sale	Physical and sellable stock fall	New sellable quantity
Web order	Reservation is created	Quantity according to reservation policy
Inspected return	Stock rises in the accepted warehouse	Updated sellable quantity

Begin with one warehouse and ten critical SKUs

Pilot one warehouse, one till and ten high-risk products. Do not expand until the movement ledger remains consistent under latency, duplicate delivery and connection loss.

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Ecommerce website and POS inventory synchronisation