Hello piwko4 -
We are unrelated to eBay, so there may be differences in the price for shipping labels that they offer compared to what we offer and there is no way to sync their label service within an Auctiva account, as the are unrelated to one another.
I am uncertain what you refer to when you state that First class requires a special service via our listing creation page - I understand that Delivery Confirmation is an option you can add when mailing first class (which is a signature required at delivery) and as such should have a tracking number, but I am uncertain where you are encountering that this would be required. If you have questions regarding USPS tracking information compatibilities, please check the USPS website or contact them directly.
I strongly suggest that you file a support case from under the Help tab of the site letting us know where you are encountering it and an example listing you are encountering it with that is in your account so we can look into this directly for you.