Before connecting a stock system to an online shop, agree what “in stock” means. A physical item on a shelf is not necessarily available for the next customer to buy.
The connection needs to understand the product variant, the location and whether some units are already promised or held aside. Copying the largest number you can find is an easy way to offer stock you cannot supply.
Work through a real stock position
Take this fictional retailer's example. It has 20 identical lamps at one warehouse. Five are allocated to unfulfilled orders and two are held for inspection. That leaves 13 potentially available for new sales, assuming no other restrictions apply.
Shopify's inventory states guide distinguishes on-hand, available, committed, unavailable and incoming quantities. Other stock systems use their own terms. The point is to map their meaning, not assume matching labels represent the same calculation.
Do not count an incoming delivery as sellable before your agreed receiving process makes it available.
Match the item and the place
A product name is not enough if the shop sells sizes, colours or packs. Keep a stable mapping between each variant and its source stock record. Check whether a pack of six is represented as one sellable unit or six components.
Map locations too. A warehouse, a retail branch and goods held by a supplier may have different fulfilment rules. Stock at a location that cannot fulfil an order should not automatically increase the website's offer.
Write down where quantity changes originate. If both the shop and warehouse system independently subtract the same order, the business can lose stock twice on paper.
Show the complete order cycle
Ask for a demonstration that follows an order through reservation, fulfilment, cancellation and return. A refund does not necessarily mean an item has arrived back in saleable condition.
Test two customers trying to buy the final unit, a part-shipped order, an order cancelled after picking and a return placed in a damaged-stock area. Also make a manual stock correction and show which system is allowed to replace the previous number.
These checks establish behaviour for the tested setup. They do not prove that every sales channel will always agree instantly.
Plan for a delayed update
Choose how much delay the business can tolerate and what action follows a discrepancy. A safety allowance may be useful in some operations, but it should be an explicit business decision rather than a number hidden in the connector.
Shopify's webhook guidance says delivery is not guaranteed and recommends reconciliation checks. For a stock connection, that means periodically comparing the relevant records and making discrepancies visible.
When the connection is unavailable, staff need to know whether to pause a channel, review low-stock orders or use another agreed process. The answer depends on your operation.
Keep a record of the quantities and rules used in the test. The useful outcome is that staff can explain why the website offers a particular number, and can find and correct a disagreement before making another promise to a customer.