If you still feel the need to resolve it properly, then I'd recommend contacting DJI support and explain the dilemma, as it appears you still have communication with the original owner who wishes to unbind it, unlike a found drone where DJI won't...
Well, I’ve never heard of this issue before and putting myself into the buyers shoes, even to me, it would sound like a scam. I myself didn’t believe the previous owner until I saw everything for myself. Also, it might be an issue with future...