How to update available products in real time for a ecommerce website

We have an eCommerce application.Let's say an "ItemA" is available and the quantity is 10. Many people are trying to buy the same product. How do we manage the availability of product in the website? When do we remove the product from website. Say, around 8 people are trying to check-out "ItemA". Many might cancel later as well. What is the general strategy that companies follow in this case?