When the shop and the website disagree about stock

A customer buys online, and an hour later you email to say it has gone. Overselling is rarely a staff problem. It comes from systems that only talk to each other once a night. Here is how stock gets out of step, and how to keep it right.

Few things annoy an online customer more than paying for something and being told, a day later, that it is not available. For a retailer with shops and a website, it happens more often than anyone likes, and the usual response is to blame whoever forgot to update the stock.

In our experience the people are rarely the problem. The systems are working exactly as they were set up: separately.

How stock gets out of step

A typical small retailer has three places that count stock: the till system in each shop, a warehouse or back-room spreadsheet, and the online store. Each keeps its own number. They are brought into line by an export that runs overnight, or by somebody updating them each evening.

Between those moments, every sale, delivery, return and transfer changes one count and not the others. On a quiet day the drift is small. On a Saturday, or during a sale, the website can be hundreds of sales out of date by the afternoon. The last unit sells twice, and somebody has to write the apology.

The hidden cost: buffers

Most retailers respond by holding a buffer: if the till says three, the website says one. It reduces overselling, but it means the website shows items as sold out that are sitting on the shelf. Those are sales you never see, because the customer simply goes elsewhere. It is the more expensive side of the same problem, and it is invisible in every report.

A stock buffer stops overselling by hiding stock you actually have.

What reliable looks like

  1. One count A single place holds the true stock figure for each product and location. Every other system reads from it.
  2. Every event Sales, deliveries, returns, transfers and corrections all update that count as they happen, not at the end of the day.
  3. Minutes, not hours Every channel follows within a minute or two. For most small retailers that is enough to make overselling rare.
  4. Alerts on drift When two systems disagree, someone is told straight away, rather than finding out from a cancelled order.
  5. Counts that are checked Regular spot counts of fast sellers, recorded in the same place, so the true figure stays true.

Do you need a new system?

Usually not. Most till systems and online stores have ways to send and receive stock changes as they happen. What is missing is the small piece in the middle that listens to all of them, keeps the one count and handles the awkward cases: a sale on a product that does not exist online, a return to a different shop, a delivery that arrived short.

That piece is the kind of thing we build in a few weeks. It replaces nothing you already use.

Where to start

Before changing anything, find out how bad the drift is. For two weeks, record every order you had to cancel or delay for lack of stock, and every product you found on the shelf that the website said was sold out. Those two lists tell you the size of the problem, and which products matter most. Fast sellers with few units are where both kinds of mistake happen.

Questions people ask

Is a stock buffer a good idea?

It stops some overselling by hiding stock you have. A shared count that updates on every sale does the same job without hiding anything.

How often should stock sync?

On every change, not on a timer. A timer leaves a window in which the last item can sell twice.

  1. Inventory Record Inaccuracy: An Empirical Analysis, N. DeHoratius and A. Raman, Management Science 54(4) (2008)

Overselling more than once a week? Tell us which till system and online store you use. We will tell you how they can be kept in step, and roughly what it would take.

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