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Inventory Management Tips for Webshops and Marketplace Sellers

2026-07-14 · 5 min leestijd

Running out of stock on a bestseller is one of the most expensive mistakes you can make as an online seller. You lose the sale, the customer may buy from a competitor instead, and on marketplaces a stockout can even hurt how often your listing gets shown. If you sell through your own webshop and one or more marketplaces at the same time, keeping stock levels accurate becomes even harder. These practical tips help you avoid stockouts and manage inventory across every sales channel.

Why a Stockout Costs You More Than One Sale

The most obvious cost of a stockout is simple: a customer wants to buy your product, it's not available, and you lose the sale. But that's rarely where it stops. A customer who hits a sold-out page often doesn't wait for you to restock — they buy the same product from a competitor instead, and there's a good chance they'll go there again next time.

On marketplaces the impact goes further still. Platforms like bol.com reward sellers who keep their offers reliably in stock, and they penalize sellers who don't. Run out of stock too often and your listing can drop in search results, lose the buy box, or get flagged for poor performance — even after you're restocked. In other words, a stockout doesn't just cost you today's sale; it can quietly reduce your visibility for weeks afterward.

The common thread: the cost of a stockout is almost always higher than the cost of holding a bit of extra stock. That's exactly why the rest of this article focuses on preventing stockouts before they happen, rather than reacting to them.

The Challenge of Selling on Multiple Channels at Once

Selling through just your own webshop is relatively easy to manage: one system, one stock count, one source of truth. The moment you add a marketplace — or several — that simplicity disappears. Now the same product can sell on your webshop, on bol.com, on Amazon, and through Shopify or WooCommerce, often within minutes of each other.

Without a central connection between those channels, your stock counts drift out of sync almost immediately. A product sells on your webshop, but the marketplace listing still shows the old quantity. A customer orders it there too, and suddenly you've sold an item you don't have. That's an oversell: an order you have to cancel, refund, or fulfil late, along with an apology email and, on marketplaces, a hit to your seller rating.

The more channels you add, the faster this problem compounds. Manually updating stock counts across platforms works for a handful of products and a handful of orders a week — it stops working once you're selling dozens of SKUs across three or four channels simultaneously. For more on why sellers add multiple channels in the first place, and what it takes to manage them well, see our article on the benefits of selling on multiple channels.

Working with Safety Stock and a Reorder Point

Reordering only once a product is already sold out is a reactive approach — by the time you notice, you've probably already lost sales. A better method is to work with two simple concepts for every product you carry:

• Safety stock: a minimum buffer you always want on hand, to absorb unexpected demand spikes or a late delivery from your supplier
• Reorder point: the stock level at which you place a new order, calculated so the replenishment arrives before you dip into your safety stock

In practice, your reorder point depends on how fast a product sells and how long your supplier takes to deliver. A product that sells five units a day with a two-week lead time needs a much higher reorder point than a slow mover with a supplier around the corner. Review these numbers periodically, especially for seasonal products or items running a promotion — demand during a sale can be several times your normal average, and a reorder point set for a quiet month won't protect you during a busy one.

Setting a safety stock and reorder point per product turns inventory management from guesswork into a repeatable process, and it's the single most effective habit for avoiding stockouts on your bestsellers.

Periodic Stock Counts and Checks

Even with good processes in place, the stock number in your system and the stock actually on your shelf can drift apart over time. Damaged goods, picking errors, returns that were never logged correctly, or a supplier delivery that was short a few units — all of these create small discrepancies that add up if you never check for them.

A periodic stock count, whether that's a full count once a quarter or rolling counts of your top sellers every week, catches these discrepancies before they turn into a stockout you didn't see coming or, just as damaging, into overselling a product you thought you still had. For fast-moving products, count more often; slow movers can go longer between checks.

If you want general guidance on the administrative side of running a webshop as a Dutch entrepreneur, including recordkeeping obligations, business.gov.nl is a useful government resource to check alongside your own inventory process.

How slimzaak Keeps Your Stock Automatically in Sync

The tips above work best when they're backed by a system that actually keeps your stock numbers accurate across every channel, in real time. That's exactly what slimzaak's inventory management is built for: it connects your webshop and your marketplace accounts — including bol.com, Amazon, Shopify, and WooCommerce — so that a sale on any one channel is automatically reflected everywhere else.

With stock synced centrally, you no longer have to manually update quantities on every platform after every order, and the risk of overselling drops dramatically. slimzaak also gives you a clear, real-time view of stock levels per product across all your channels combined, so you can spot a product approaching its reorder point before it actually runs out, instead of finding out from a cancelled order.

You can start using slimzaak for free on the ZZP plan (€0/month), connect your channels, and see your combined stock levels in one place from day one — no credit card required.