Yes, indeed. My question is if the NFT will be treated as a valid proof of ownership in a legal battle. I’m guessing it would hold some validity, but lose against a well-written sales contract.
You're either transferring ownership of the copyright or not. Hopefully that's clear when they're traded otherwise neither party will have any idea if they're getting completely ripped off or not. If it's not clear then you probably aren't. Though, some countries' copyright laws allow ownership to be transferred without being explicit about it through the (imo yucky) commissioned work exception.