Ownership transfer is done by a function call. The function often has extra logic like % of the funds for the transfer going to the artist. I guess you can cheat by sending a small amount in the transfer and seperately paying the seller the rest but then you make the thing you bought seem cheaper in the official records so that's in most cases counter-productive.
So I guess the next goal here is a startup to implement this as a smart contract to go full circle. The market will do it because any transaction fee is a hindrance to it's liquidity and is a possibility to undercut someone else.
