Ebay fees are around 13.4% (depending on category) and have been for years. You will pay more if you promoted the listing, however.

All online commerce platforms charge in excess of 13%, so I'm not sure why you feel Ebay should be the exception?

The fact that you undercharged the buyer on postage is hardly Ebay's fault!

Nobody is forcing you to sell here, but when you do, you accept all the Terms and Conditions, which includes the fees and which are fully displayed for you to review before listing anything.