Relist when Quantity is Less or Equal to 1 and Stop When Quantity Is 0 are the default and recommended settings. They are meant to optimize the product data updating process when MSI mode is on. Let’s see how it works.
When you set Any for Relist when Quantity or No action for Stop When Quantity Is options, M2E Pro system ignores QTY values and reacts only to the status change — Out of Stock or In Stock.
When Magento Order is placed, the multi-source Magento module reserves product quantity by itself. It decreases product Salable Quantity from the Stock. At this point, the product is still In Stock. Only after a Shipment is created, Magento deducts Product Quantity, and then the item status changes to Out of Stock.
At the point when Salable QTY is 0, but Product QTY is still 1, another user on a Channel may try to make a purchase. If you set No action for Stop When Quantity Is an option, M2E Pro will ignore QTY and wait until the item status changes to Out of Stock to stop it. This may cause oversell.
However, in case you set default Stop Rules, M2E Pro detects 0 QTY value and the item will be Stopped.