One of the issues e-commerce operators most want to avoid is 'overselling'—the state in which an order goes through even though the item is out of stock. It forces you to apologize to the customer, refund them, or offer a substitute, and it dents trust in the brand. Once it happens, it is the kind of incident that exhausts everyone involved.
And yet, overselling is the kind of trouble that is hard to drive 'absolutely to zero.' E-commerce is a world where orders come in from multiple paths at the same time. A moment's delay, a missed setting, a discrepancy with an external system—various factors stack up. In this article we organize the patterns under which overselling occurs and lay out the preventive measures you can take from the side of a sheet-sync tool like Sync Master.
Patterns in which overselling occurs
Overselling has several typical patterns. Pinning down where the cause lies surfaces the right countermeasures.
- Sync lag: actual inventory has dropped, but Shopify's number is still old
- Multiple channels: physical store, Amazon, Shopify, etc. share the same inventory but lag in syncing to each other
- Missed location settings: 'continue selling when out of stock' is still on for locations without inventory
- Insufficient buffer: with 1 unit in stock, two orders come in at the same time (a so-called race condition)
- Missed manual updates: the actual count changes at stocktake but no one updates the sheet
If your store has experienced overselling in the past, think back about which of the patterns above applied. If it has happened multiple times, chances are good the same pattern is repeating.
Sync lag and insufficient buffer
Sync lag and insufficient buffer are especially tricky. No matter how high-performance the tool, there is always a small time lag between the value reaching Shopify from the sheet. On an hourly sync schedule, in the worst case you can get a 59-minute lag.
The technique to absorb this lag is the 'buffer.' Even if actual inventory is 10, you write 8 to Shopify—the idea is to give yourself a two-unit cushion. It is also called safety stock. Too much buffer means lost sales opportunities; too little buffer makes overselling more likely. You need to find the right buffer per product and per season.
Tips on setting buffer
Setting buffer like 'a flat 2 units for every product' is simple but inefficient. Fast movers and barely-moving items need very different buffer levels. Pulling values like 'average daily sales' or 'sales in the last 7 days' into the source-of-truth Google Sheet and dynamically deriving buffer from them gives you a much more nuanced operation.
For example, with IF or ARRAYFORMULA you can implement 'if daily sales are 5 or more, buffer 3, otherwise 1' as a single column. Because Sync Master simply reflects the values written in the sheet to Shopify, applying these techniques on the sheet side makes Shopify's inventory smarter as a result.
What Shopify settings can prevent
The basics of overselling prevention start with getting Shopify's settings right. Here are items that are surprisingly easy to miss.
- 01Enable 'Track quantity' for each product
- 02Choose 'stop selling when out of stock' (the default may be 'continue selling')
- 03Restrict sales by location and remove unneeded locations from products
- 04If you have in-store POS or external channels, review the inventory-sharing settings for each
Item 2, 'stop selling when out of stock,' is especially important since leaving it at the default can let overselling happen. You can toggle per product whether to accept orders beyond actual inventory, so for anything other than digital goods or dropshipping, set it to 'stop' as a rule.
Techniques on the sheet-sync side
With Shopify settings in order, adding techniques on the sheet-sync side pushes the probability of overselling down even further.
- Raise sync frequency as much as possible (every 15 minutes lags less than once an hour)
- Add a buffer column on the sheet and send the buffered value to Shopify
- At the start of a sale or just after restocking, run a manual instant sync
- For best sellers, highlight an alert row just before stock hits zero
- Make sure failure notifications arrive on Slack or email
'Raise sync frequency' sounds simple, but the impact is large. Choose a tool, like Sync Master, that supports frequent syncs and is designed to allow you to push the frequency up; you will find yourself panicking less. That said, raising frequency too far can hit API limits, so it is also worth checking whether the tool handles that intelligently for you.
Wrap-up: zero is hard, but you can get arbitrarily close
Realistically, reducing overselling to zero may be difficult. But by understanding the patterns of root causes, getting Shopify's settings right, and stacking up techniques on the sheet side around buffer and sync frequency, getting arbitrarily close to zero is possible.
If you have experienced overselling in the past, pull up the logs from that time and look back at which pattern it was. A sync tool like Sync Master keeps logs that you can use for exactly this kind of retrospective. Once the cause is clear, the countermeasure will always reveal itself.