Before automatic update, products that come from your product source are compared with products that you have listed on virtual marketplaces. After this comparison, products that changing in fields like product name, description, stock amount, price, image etc. are updated automatically.
If you have new products on your product source, those products are added to virtual marketplaces. If product stock items go below minimum stock item, those products will be deleted from virtual marketplace. If there is a change in product information, update is done on changed areas.