When you sell an item on eBay, the seller is responsible to get the item to the buyer. In most cases, the seller will ship the item.
Since it is the seller responsibility to get the item to the buyer, the seller purchases the label from the carrier and pays for that label.
When the buyer pays for the item, the buyer "Pays" shipping, but that payment goes to the seller to use for shipping. They are not responsible for buying the label for shipping so the money is transferred to the seller and the seller uses the funds for shipping.
So buyer pays shipping to the seller, Seller buys label from the carrier.
