Multichannel e-commerce: marketplaces without the overselling

Multichannel e-commerce means selling the same stock through your own website and through marketplaces such as Amazon, eBay and TikTok Shop, with one system holding the true stock figure and pushing it to every channel. Get that one thing right and marketplaces are extra revenue. Get it wrong and you sell items you do not have, cancel orders and lose your seller ratings.

The software that does this job is usually called a multichannel or order management system. Linnworks, Rithum (the company that used to be ChannelAdvisor), Brightpearl and Veeqo are the names UK sellers meet most often. For a small catalogue on Shopify, a connector app is often enough to start.

Our advice is to add channels one at a time, decide which system owns stock before you list anything, and work out your margin after fees on each channel. Revenue from a marketplace is easy to win and easy to lose money on.

The short version

• One system must own the stock figure, and every channel must take its number from that system.
• Amazon and eBay are open to almost any seller, while retailer marketplaces such as Tesco, B&Q and Debenhams choose who they let in.
• Expect to give up roughly a tenth to a fifth of the sale price in marketplace fees before fulfilment and advertising.
• A connector app suits one or two marketplaces and a simple catalogue, and a full order management system earns its cost once you have several channels, a warehouse team or kits and bundles.
• Overselling is nearly always caused by slow stock updates, stock held in two places, or bundles that are not broken down into their parts.
• ChannelAdvisor still exists, but it has been part of Rithum since 2023 and is aimed at larger brands and retailers.

Which marketplaces matter for a UK seller?

Start with where your customers already shop. For most product categories that means Amazon first, then eBay, then the specialist or retailer marketplace that fits your range. TikTok Shop is different: it sells through video and creators, so it works for products that demonstrate well and fails for products that need explaining in a specification table.

Fees change most years. eBay raised its per-order fee on orders over £10 in February 2026, and the others revise theirs regularly. Check Amazon's pricing page and eBay's business seller fees before you build a margin model, and remember that if you use Fulfilment by Amazon you pay fulfilment and storage fees on top.

If you already send stock to Amazon, its Multi-Channel Fulfilment service can also send out orders from your own website, and there is a Shopify app for it in the UK. That gives you one pool of stock for both channels, at the cost of depending on Amazon for your own customers' deliveries.

What does multichannel software actually do?

Four jobs, and it helps to know which ones you need before you watch a demo.

• Listings: it takes your product data and publishes it to each channel in the format that channel demands, including categories, attributes and variations.
• Stock: it holds one figure per product and updates every channel when a sale, a delivery or a return changes it.
• Orders: it pulls orders from every channel into one queue, so the warehouse picks from a single list.
• Shipping: it chooses a courier by rule, prints the label and sends the tracking number back to the channel.

Some tools are strong on listings and data feeds and light on the warehouse. Others are the reverse. That difference matters more than the feature grid.

Linnworks, Rithum and the alternatives

For most UK retailers with their own stock room and three or more channels, we would start by looking at Linnworks. It began in the UK, the warehouse tools are practical, and it connects to the couriers British sellers use. It is also the tool we implement most, so weigh that. When Rat & Boa's stock was scattered across channels with no single system, we brought their orders and stock into Linnworks and added shipping rules, and stockouts fell by 75%.

It is not always the answer. If you sell on Shopify plus Amazon only, try Marketplace Connect first and keep the money. If your problem is product data for dozens of retailer feeds, a feed specialist such as Feedonomics or Rithum is a better fit than a warehouse tool. If you want finance and stock in one place, look at Brightpearl or a full ERP, and read our guide to e-commerce integrations before you choose.

How to avoid overselling

Overselling happens when a channel still shows stock that has already gone. The fixes are operational more than technical.

1. Name one stock master. It can be your order management system, your ERP or Shopify. It cannot be two of them. Every other system reads from it.
2. Check how fast stock updates travel. Ask each vendor how often it pushes stock to each channel, and test it. A sync every 15 minutes is fine for slow lines and dangerous for a product in a TikTok video.
3. Hold back a buffer on fast or low-stock lines. Showing two fewer than you hold on marketplaces costs little and prevents most cancellations.
4. Break bundles into components. If a gift set uses three products, selling the set must reduce all three. Check this before peak, with a real order.
5. Keep Amazon-held stock separate. Stock in Amazon's warehouses is not available to your own pickers, so it needs its own location in the system.
6. Book returns and deliveries in promptly. A pallet sitting unbooked at goods-in is stock you cannot sell. A return added back before inspection is stock you should not sell.
7. Count regularly. No system fixes a shelf that does not match the screen. Count a few locations every day, not everything once a year.

Common mistakes

• Listing everything everywhere. Low-margin lines can lose money once fees, delivery and returns are counted. List the products that still make money on that channel.
• Ignoring the cost of advertising. On Amazon in particular, sponsored placements are close to compulsory in busy categories. Model them as a cost of sale. Our ROAS profitability calculator helps with the break-even sum, and our Amazon marketing team sees this daily.
• Buying the big system too early. An order management system takes weeks to set up properly and needs someone to own it. Below a few hundred marketplace orders a month, a connector app is usually enough.
• Undercutting your own website. If the marketplace price is lower, customers learn to buy there, and you pay commission on a sale you would have had anyway.
• Assuming you have to be on marketplaces at all. Some brands are right to stay away: made-to-order products, items where your own customer relationship is the value, or ranges where a marketplace seller will always be cheaper.

How we'd approach it

We start with a margin table by product and channel, using the current fee pages, your delivery costs and a realistic returns rate. That usually cuts the planned listing range by a third or more.

Next we map where stock lives today and agree the single master. For the Aquinos Group, owners of Gato Preto, we set up Linnworks as the link between Microsoft Dynamics 365 Business Central and their Amazon and Shopify channels, with onsite training so their own team could run it.

Then we launch one channel, run it for a month, fix the exceptions and only then add the next. Our logistics consultancy covers the warehouse and courier side, and our integrations team handles anything the standard connectors do not.

Questions we get asked

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