eBay Out of Stock Control allows you to keep a GTC (Good ‘Til Canceled) item alive, even when the quantity goes to zero. This feature allows you to keep the same item identification without the need to relist the item when it’s back in stock.
The benefits to you are easier inventory management, item identification history (used for search engine optimization and merchandising), sales history retention, and easier item variation management.
To set Out of Stock Control, click on Settings > Channels, and then expand the eBay Options section. Then scroll down the page to the “Out of Stock Control” field and toggle it to On or Off.
Note: when you choose to have this feature on, you must disable or delete the item to end the listing.
Out of Stock Control can also be set for individual items on the editor page. The field will show up only if Listing Type is set to "FixedPriceItem" and Listing Duration is set to "Good Till Cancelled". It will be set by default to whatever value you have selected for it in Settings > Channels, in the eBay Options section.