Select the active listing and switch to “Live” mode. In the Inspector on the right you’ll find the listing fees.
No. You don’t pay additional eBay fees if you’re using GarageSale.
Almost certainly you will not be charged. eBay’s API is notoriously bad when it comes to computing fees upfront. For some reason, the ignore there own policies and never give the correct price when the seller has a free quota.
My advice is to list a single listing with GarageSale, ignoring the whatever fees GarageSale shows you before and after the listing. Right after the listing go to the eBay website and verify that the listing was indeed free to list.
That’s a warning from the eBay system (not from GarageSale). Could you send me a screenshot so we can see what you see? Maybe you didn’t select PayPal in your payment options in your listing?