Total fees have worked out about 13% for years now, although it can vary, depending on what category you're selling in. Ebay have also taken a percentage of the shipping cost for at least the last 10 years +.

In the early days, sellers just paid a fee on the item only when it sold, so I remember seeing items for $1.00 in cost and $500 in postage (for example). Eventually Ebay figured it out and changed it so that the percentage applied to the total.

Most selling platforms charge a fee for the entire transaction and many sellers charge a little higher in postage to account for the fee that is taken.