Sold at the counter, and off the website about a minute later.
Nobody sets out to advertise something they already sold. It happens because the two live apart.
The failure nobody notices until a customer does
The website says a thing is available. The shop sold it on Saturday. The first person to find out is somebody who travelled in, or who waited for a reply, and that is the worst possible way for it to come out.
Nobody is being careless. The two systems were never introduced.
How it works at Iglisi Watch
A watch sold over the counter stops being offered on the site about a minute afterwards, and nobody opens a laptop to make that happen. The sale is recorded where the sale is, and the site follows.
Adding one runs the same machinery the other way: the product page, the shop list, the sitemap and every figure written into the surrounding text all move together, in all 3 languages.
Why about a minute, and not instantly
Instant costs more than it is worth here. A minute beats anybody walking to a laptop, and building for a minute means the thing keeps working when the internet in the shop does not.
Choosing the looser number deliberately is usually what makes small software reliable.
What it takes to have this
One place where a sale is recorded, and one rule for which side wins when the two disagree. Most of the work is deciding that rather than writing it.
If your website and your shop already disagree, tell us where. The answer is often one rule rather than a rebuild. Get a free audit.
Updated