IF the stock system shows 5 in stock… there’s 5 in stock… what a bloody rubbish system that doesn’t show live updates.
Believe it or not an online shop is still run by people.
The systems are automated with stock to a degree, but a sale has to go through stock allocation (that piece of stock against that customer), credit control (taking the details you’ve input on the web and assuring the money has been taken), warehouse (Finding the goods), and shipping (packing and loading the goods).
Unfortunately in these stages are humans, which work quite a bit slower than computers. A piece of stock might not be shown as “sold” until the item passes credit check in their accounts, and at the rate at which these were sold a number of order could be submitted in that time whilst it still shows stock on the website.
Whilst a lot of online shops run a very well oiled, tight operation – there are still humans and a warehouse behind the pretty website.