I don't think he's greedy. 15% of appreciated isn't that much: assuming the current auction settles for $2500, and in the next auction it sells for $2600, then that's only $15. I suspect agent's fees are usually a % of total, not a % of the diff. And if in the subsequent auction it sells for $2400, then that's $0 commission.

The contract declares the box to be no longer "A Work Of Art" should the contract terminate. But I don't think that means it's worth nothing. Ex-works-of-art are pretty rare.

Who here knows about an art work titled "Erased de Kooning Drawing" ?