When you’ve found a product idea you believe in, it’s easy to get swept up in names, plans, and launches. But most ecommerce problems don’t come from the big picture. They come from small, repeated mistakes that add up: a stock count that’s wrong, a delivery that’s late, a spreadsheet that’s out of date.

Here are seven of the most common mistakes ecommerce sellers make, with what to do about each one.

1. Buying on instinct instead of data

It’s tempting to buy products you like, or products that are exciting to you, rather than products your customers want. A line you’re passionate about that doesn’t sell quickly just becomes cash sitting on a shelf.

The fix: let sales data guide your purchasing. Look at what sold, when, and on which channels, and account for seasonal peaks. Use demand forecasting to decide how much to buy, and see our guide to finding profitable products before you commit to a new line.

2. Letting slow stock sit

Unsold stock isn’t neutral. It ties up cash that could pay for better-selling products, marketing, or improvements, and it costs money to store. The longer it sits, the harder it is to sell at a decent price.

The fix: decide early what to do with slow movers. Discount them, or bundle them with best sellers, which is easy if your inventory system supports kits and bundles. Then reassess, and if they still don’t move, clear them. See our guides to dead stock and inventory reduction strategies.

3. Relying on spreadsheets and manual work

A spreadsheet is a sensible way to start. But as you add products, channels, and orders, manual tracking gets slower and less accurate, and mistakes such as mis-ships and returns cost you time and money. It also leaves you without reliable data for decisions.

In the State of Commerce Ops 2026 report, reporting, returns management, and exception handling were the least automated areas, with around one-third of retailers still relying heavily on manual work.

The fix: move the repetitive, error-prone jobs to software: stock updates, order routing, shipping selection, and reporting. Start with the task that eats the most time. See where to start with ecommerce automation.

4. Not keeping stock in sync across channels

When you sell in several places, an item can sell out on one channel while it still shows as available on another. The result is overselling: cancelled orders, unhappy customers, and, on marketplaces, penalties that can include losing selling privileges if it happens repeatedly.

Stock accuracy is a common weakness. In the same State of Commerce Ops report, only about a third of retailers rated their inventory visibility across channels and warehouses as excellent (33.2% in the UK and 37.2% in the US).

The fix: keep one central record of stock and sync it to every channel automatically. See our guides to preventing overselling and reducing stockouts, and our guide to inventory control problems and how to fix them.

5. Being slow to receive and list new stock

Receiving and processing often get less attention than picking and shipping, but delays here cost real money. Every day new stock sits unlisted is a day it isn’t earning. If you have 30 days to pay a supplier invoice and spend two weeks receiving and listing the goods, you’re left with two weeks to sell enough to cover the bill.

The fix: treat the supplier invoice as a clock. Set a target for how quickly goods are received, checked, put away, and listed, and track it.

6. A weak shipping and returns experience

Shipping is the last step of the sale and often what customers remember. A single shipping option, no delivery date, manual carrier selection, and a confusing returns process all add friction and cost.

• Offer choice. Different customers want different speeds and prices, and some options can win sales you’d otherwise lose.
• Automate carrier selection by cost, service, and destination, instead of choosing by hand. See our guide to getting better shipping rates.
• Show delivery dates and costs before checkout, and send tracking updates afterward.
• Plan for returns. NRF and Happy Returns estimated that 19.3% of online sales would be returned in 2025, and 82% of consumers said free returns influence where they shop. Detailed listings and careful packing prevent avoidable returns. See our guides to reducing returns and returns management.
• Reduce mis-picks. The wrong item shipped is one of the quickest ways to lose a customer. See our guide to preventing picking errors.

7. Depending on one channel, and running without processes or KPIs

One channel. Relying on a single marketplace or product line leaves you exposed if the platform changes its rules or fees, or if demand shifts. In the State of Commerce Ops 2026 report, the average retailer sold on 4.15 (UK) and 4.25 (US) marketplaces or channels, and retailers with broader channel coverage were more likely to report growth. Each channel reaches different shoppers, so adding them can grow sales, as long as you can manage the extra complexity. See our guide to selling on your own website vs. marketplaces.

No processes or KPIs. Founders often do every job themselves at the start, but that doesn’t scale. Write down how routine tasks are done, such as receiving, counting, picking, packing, and returns, so others can do them the same way, and track a few KPIs for each area. See our guide to inventory KPIs. It frees you to work on the business and not just in it.

One more to watch: your suppliers. Treat them as partners. Reliable, honest relationships often bring better prices, better terms, and more flexibility when things go wrong.

How Linnworks helps

Linnworks connects inventory, orders, and shipping across 100+ native channel integrations, and syncs stock in under 10 minutes, which covers most of the mistakes above in one platform. See inventory management and multichannel selling, or request a demo.

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