Delivery Details in your eBay listing
When you create your eBay listing you decide the postage cost and service, go the the section "Delivery Details" . The amount and the service you select in your eBay listing will be the amount and the service your buyer will pay and use for the postage service.
Shipping cost in eBay Delivery
When you then click on print postage label, then the amount you had assigned into your eBay listing will be reflected into eBay Delivery. Click on print postage label then review the Buyer paid of delivery section as below: