I sold an item on eBay with FedEx Ground as the preferred Shipping Carrier and when the buyer paid, I went to print out the shipping label. It only gave me USPS options and would not allow me to access another carrier. The buyer paid for the FedEx shipping. I contacted eBay support because I have 3 business days to get the item out to the buyer. eBay support (AI) contacted me after 24 hours and said I could go in and change the carrier to FedEx, again it would only bring up USPS. I did a search...

Disputing Additional FedEx Shipping Charges | Ask a Mentor

Disputing Additional FedEx Shipping Charges | Ask a Mentor | eBay Community