Selling on more channels without selling stock you don't have

The first marketplace is easy. The second is where it starts to hurt, because now the same box on the same shelf is for sale in two places, and only one of them knows when it's gone.

If you sell physical products, adding channels is one of the most obvious ways to grow. Your own website, a big-name marketplace like B&Q, perhaps Amazon or eBay later. More shop windows mean more customers. But every new channel adds a question that is surprisingly hard to answer: how many do we actually have?

How overselling really happens

Nobody sets out to sell stock they don’t have. It happens because each channel keeps its own count, and someone (or something) has to keep those counts in step.

Here’s the usual sequence:

1. You have three units left. Your website says three, the marketplace says three.
2. One sells on the marketplace. Your website still says three.
3. Someone buys two on the website. You’ve now sold four units from a stock of three.
4. A person apologises to a customer, issues a refund and, if the marketplace is involved, takes a hit on their seller rating.

The fix most businesses reach for is a person with a spreadsheet who updates every channel each morning. That works until the day it doesn’t: a busy Monday, a sick day, a flash sale. Stock that changes by the hour can’t be managed by a task you do once a day.

The principle: one number, everything reads from it

Every reliable multichannel setup we’ve seen follows the same rule. There is one source of truth for stock, and every channel reads from it. Nobody types a stock level into a marketplace. They change the real number in one place and the rest follows.

For many UK small businesses, that one place is already Xero. It already holds your products, your sales and your purchases, so it’s a natural home for the number that matters. The job is then to:

• Push stock out. When the number in Xero changes, the website and each marketplace listing update automatically.
• Pull sales in. When an order lands on any channel, it’s recorded once and the stock figure drops.
• Take payment cleanly. On your own site, card payments go through Stripe and are matched to the order, so finance isn’t reconciling by hand.
• Fail loudly. If a sync breaks, someone is told straight away, not three weeks later when a customer complains.

That is how we built the SPC flooring marketplace: a website selling across the UK, connected to Xero, Stripe and the B&Q marketplace, with stock managed in Xero and no manual updating of stock levels.

What to ask before you add a channel

Before you sign up to another marketplace, run through these questions. Each one is cheaper to answer now than after launch.

Where does our stock number live today? If the honest answer is “in a spreadsheet, and in Dave’s head”, fix that first.

How quickly does a sale need to show up everywhere? Fast-moving, low-stock lines need near-instant updates. A slow-moving range with plenty of stock can be more relaxed.

What happens at zero? Decide up front whether listings should switch off automatically, and whether to hold back a small safety buffer so the last unit isn’t on sale in three places.

Does the marketplace need approval? Some, B&Q’s included, vet sellers before you can connect, so build that lead time into your plan.

Who gets told when something fails? A sync with no alerting is a sync you’ll discover is broken from a customer’s email.

Bought connector or custom build?

There are off-the-shelf tools that connect marketplaces to stock systems, and for a simple setup they can be the right answer. We’ll tell you if that’s you. A custom integration earns its place when:

• your stock logic is unusual (made-to-order lines, pack sizes, bundles);
• you want your own storefront with your own checkout and no per-order commission;
• the accounting side needs to be exactly right in Xero, not approximately right;
• you’ve outgrown the monthly fees of stacking several connectors.

Either way, the point is the same: stock should be managed once, by the system, and never by a person typing numbers into three dashboards.

What it’s worth

Overselling costs money in refunds, in lost seller ratings and in staff time spent apologising. Manual stock updating costs money in hours, and it gets worse the more you grow. Use the same sum from The £40,000 spreadsheet: hours per week, times people, times cost per hour. For a growing multichannel seller, “keep the channels in step” is often the single biggest line.

Thinking about adding a channel?

If you’re about to open a second or third sales channel, or you’re already feeling the strain of the first two, get in touch. A short discovery sprint will map where your stock number lives today and what it would take to make it true everywhere.