Are you losing your customer when there's "Soldout" button on product, convert "Soldout" to "Notify Me" Or "PreOrder" button and know about your products demands, Your customer can ask for the product restock notification and whenever you restocked the product the email notification will be sent to the customer. Create new customer on your store and increase marketing strategy, also filter products by notify tags and get notification on new notify leads. Start sales before items are in stock.