As for the crypto Ebay, just think from a client perspective, you buy from a decentralized platform with no company behind it and pay with a non-reversible method.
A buyer's paradise!!!
This is why the argument that buyers will flock to crypto because merchants will offer them a few percents of discount just isn't that convincing to me. Consumers are ready to pay more to avoid negative experiences, and if crypto markets will have reputation for hosting scammers, there won't any huge adoption, and only hardcore crypto fans will be using them regularly.