Shoppingfeed treats the product in your Back Office as the main inventory, and keeps each product in the inventory updated on your distribution channels based on the count in your e-commerce.
When a sale occurs on one of the distribution channels, the availability of the product on the various channels will be updated, so that you can take it into account for your orders on the Shoppingfeed platform as well as on your e-commerce.
In the event that a product becomes Sold-out on one of your distribution channels, Shoppingfeed removes the product on all other channels, until inventory becomes available again.
More simply: When there are stock changes on any of your channels or in your source feed, Shoppingfeed makes the changes to keep your catalog always up to date.