I'm due to start an ecommerce site and was wondering if anyone knows of a reliable system for coordinating stock amounts across a site and shop. E.g. the customer adds a book to his site with a stock quantity of 10, 2 people go online and buy a book each, the stock is now 8, but 2 people also came into his shop and bought a book each, the actual stock is now 6 but the site is still set at 8. I could ask the customer to update his stock through the CMS as each book is sold from the shop but that would only work with very small businesses and wouldn't rule out the possibility of an online purchase being processed at exactly the same time as a shop purchase. What if any is the conventional way to deal with this?