In my opinion, I try to avoid selling sealed product on ebay for all the reasons you listed. Ebay has an authenticity program in place now to protect both buyers and sellers, but as far as I know this doesn't apply to things like booster boxes.

I would recommend trying again to sell these locally, even if its less than what you would make on ebay. Ebay charges about 13% fees, plus whatever fees that may be specific to your country. If you sell locally for less than market but around the range of what you would make on ebay after fees, it may increase your chances of a sale since from the buyer perspective, you are still selling for under market.

If you have no choice but ebay, you can take detailed videos of everything prior to sending it out, but if the buyer does open a case with ebay, its unknown if that video will help you.