Glossary
Overselling
Definition
Overselling is accepting an order for more units than you actually have in stock, leaving you unable to fulfil it. On Shopify it usually happens in the gap between a sale and the inventory update, when two shoppers buy the last unit at once or a fulfilment sync lags. The fix is a safety-stock buffer that stops selling before inventory hits zero.
Why Shopify oversells
Overselling is a timing problem. Inventory updates a moment after a sale, so simultaneous checkouts can both take the last unit, and a warehouse or 3PL that syncs on a delay leaves Shopify showing stock that is already gone.
The common workaround, quietly under-counting stock, breaks the moment a fulfilment service syncs the real number back. A safety-stock buffer is more reliable because it works from your true count.
How to prevent overselling
Set a floor for each product and stop selling once available stock reaches it, rather than selling to zero. Enforcing that floor at checkout, server-side, means it holds even on Shop Pay and direct checkout links.
See how to prevent overselling on Shopify for the full setup.
See also