In this article:
The 
badge informs you that your company has confirmed a product's availability as of that day. Note that we do not show actual inventory levels, and that the lack of a Verified in Stock badge does not necessarily mean that the item is out of stock. You should always check your company's internal systems when confirming an item's availability with a buyer.
The verified in stock functionality requires that a file be sent every business day in order to ensure the green badge remains on the marketplace.