You can right-click on that warning from eBay and let GarageSale ignore it in future.
That’s another error message from eBay. Your store categories you’re using in GarageSale seem to be out-dated. Please update them in the GarageSale preferences > Accounts (“Update Account Details”):
Sure, make sure to bulk-edit the selected listings correctly, it’s a bit tricky. Please see the help (and the animation) here:
GarageSale 7 uses so-called “PopOver” windows. They usually don’t have “OK” buttons.
To cancel the upload you can always hit the red close button of the Launch Control window. The “Cancel” button can cancel a running upload as far as I know.
Hope this helps,