I have noticed that eBay often charges buyers much more for shipping than it actually costs sellers to purchase the shipping labels through the eBay system.
Sellers are encouraged to pocket the difference, unless they want to go through all the various steps of making a partial refund to the buyer.
eBay of course gets the use of the money buyers are over-charged from the time it is received until paid out to the sellers, and generally co-opts sellers into their scam.