You sell in your online store, a customer buys the last unit you had left and, at the same time, that same item has just sold in your physical shop or over the phone. Result: you've sold twice something you only had once. That's overselling, and it's one of the most frequent -and most avoidable- problems of selling through several channels at once without them talking to each other.
Why it happens, exactly
Overselling isn't a one-off glitch or bad luck: it's the direct consequence of having stock spread across several places that don't talk to each other. If your online store, your physical till and your ERP each keep their own stock count, updated by hand or with a delay, there will always be a window where the same product shows as available in two channels at once, even though in reality only one unit is left. The faster that product moves and the more sales channels you have open, the more frequent the problem becomes, not less.
The real cost of an oversold order
It isn't just the awkwardness of having to call the customer to say there's no stock after all. Every oversold order means managing a cancellation or a delay, offering an alternative or a compensation, and absorbing the reputational cost of a bad experience right after the customer had already completed the purchase -the point in the process where a setback is least expected-. Multiplied by the orders lost this way every month, the accumulated cost is usually higher than it looks at first glance, even though each incident on its own seems minor.
The solution isn't counting more often, it's having one single source of truth
The usual temptation is to count stock more frequently or reconcile it by hand every morning across channels. It helps, but it doesn't fix the underlying problem, because there are still several systems each with their own version of reality. The real solution is that there is one single source of truth for stock -normally the ERP, since that's where every real stock movement is recorded- and that every other sales channel checks that figure in real time instead of keeping its own.
That's how it works, for example, in our Shopify and PrestaShop integrations with Business Central: the ERP centralises the real stock, counting sales from the physical shop or any other channel too, and the online store syncs against that figure almost instantly, instead of keeping its own disconnected count.
What's worth syncing beyond just stock
Stock is the most urgent part, but not the only thing worth connecting. When an order from a channel enters the ERP automatically -without anyone retyping it by hand-, on top of avoiding overselling you also remove the risk of mistakes copying addresses, references or quantities, and the order is already ready to prepare and invoice following the same flow as the rest of your sales. It's the same logic we explain in our article on the differences between EDI and API when deciding how to connect two systems: what matters isn't the specific technology, but making sure information stops depending on someone typing it twice.
Frequently asked questions
Is real-time stock sync expensive to maintain?
Once it's set up, maintenance is usually minimal, because the connection keeps working on its own without anyone needing to step in daily. The real cost is in the initial setup: defining what information travels, in which direction and how often between the ERP and each sales channel, adapting it to your catalogue and your actual logistics. From there on, the system simply keeps that sync running automatically, without generating recurring work comparable to counting stock by hand every day or reconciling spreadsheets between channels, which is exactly the manual work this sync replaces. Even adding a new sales channel later on is mostly a matter of connecting it to the same central figure, not rebuilding the whole sync from scratch.
Does it work the same way if I sell on several online stores at once?
Yes, and that's actually the scenario where having one single source of truth matters most, because the risk of overselling grows with every extra channel that isn't connected to the rest. The principle doesn't change: the ERP centralises the real stock across every combined channel, and each online store, whether Shopify, PrestaShop or any other, checks that centralised figure instead of keeping its own isolated count. The more sales channels you have open at once, the more this centralisation pays off, because the manual work of reconciling stock across all of them grows in proportion to the number of channels, not just to sales volume.
Does this also prevent order mistakes, or only stock issues?
Order mistakes too, and it's usually the second benefit that stands out most once overselling is solved. When every order from a channel enters the ERP automatically with its customer and lines already loaded, you remove the manual step of copying that data from the online store's panel into the management system, which is exactly where transcription errors creep in: a wrongly copied address, a mistaken quantity, a reference confused with a similar one. By automating that data entry, the order reaches the ERP exactly as the customer confirmed it, without the intermediate step where mistakes used to be introduced, and without anyone having to double-check it against the original order later on.
In summary
Overselling isn't solved by counting stock more often, it's solved by having one single source of truth that every channel checks in real time. The ERP is the natural place for that source of truth, since it's already where every real stock movement is recorded.
If you sell through several channels and want to stop reconciling stock by hand, check out our Shopify integration with Business Central or tell us which sales channels you have open and we'll tell you how to connect them.