EBay fees have been with us since eBay started back in 1995.
Paypal (and Billpoint before it) has had fees since the turn of the Millennium.
A 10% fee on shipping has been with us since 2011.
- It is possible in some cases to reduce the 10% by using Free Shipping and folding the cost of shipping into the asking price for a listing in a lower fee category.
Promotion fees are only charged if the item sells. The seller chooses the percentage she is willing to pay.
EBay is charging applicable sales taxes in their fees. We Canadians are charged 5%GST (federal sales tax) and applicable provincial sales taxes.
Buyers in some US states are now being charged state sales taxes which are collected by eBay. Sellers are not involved in this.
Most of those costs are known to the seller (not the buyer's sales tax of course) and are part of the price we have to mark our asking prices up from.