What you may not have realized is that your fee level is charged on your buyer's entire payment, which includes selling price, shipping fees, and the sales tax eBay collects from the buyer and remits to the buyer's state government.
So if you sell a $100 item to a buyer in a state with 5% sales tax on goods AND services* and charge him $10 shipping, his payment will be $100+$10=$110x1.05 = $115.50.
And at the usual 12.9% fee that's $14.89.
Quite often sellers misunderstand and think they are being charged more than the advertised 12.9% because they don't grasp what the fees are based on.
The other misunderstanding is that it is Standard Practice in the financial industry for payment processors** to charge fees on that ENTIRE payment.
And has been for years. We got our first merchant credit card account (Chargex) back in the early 1980s and were paying fees to the processor (Moneris) for sales and sales taxes then. And when we started our auctions (at first mail later online) we also paid on the shipping charges that were part of the buyer's payment.
Processors do not make a difference what you are being paid for, only how much they are processing for you.
FWIW - these fees are tax deductible.
Between the more transparent MP billing and the recent lowering of the level at which the IRS wants 1099 forms issued to sellers, many small sellers are realizing for the first time their side hustle is really a fun hobby.
*Services include shipping. Some states will charge for services, others don't.
** Both Managed Payments and Paypal do this.
