As others have said, the guy has either been busted by his significant other for spending money and is regretting buying it all or is a chancer looking for money off.
Either way, I’d let it go through the ebay process as you don’t have much to lose, stating that you’ve said in the listing that they go up tubeless (ie sealant will have been in them as it is required for tubeless setups) and are described as having cosmetic wear but are fully functional- residue is cosmetic and they are fully functional.
There are many other things in the listing such as scratches and minor play (not to mention the tyres being muddy , shock horror) clearly indicate they are used but fully functional as described and the sealant is exactly the same. I wouldn’t lead with saying that though 🙂