Does anyone have any experience with returning items that were not as described to private sellers on Amazon.com?

I bought a DVD from a private seller on Amazon that was supposed to be in “very good” condition. I get it and immediately notice that there’s a large crack in the disk radiating outward from the center hole. It plays just fine, but it might not work if the crack increases in size. In any case, it’s not what I would consider to be “very good” condition. The seller says that he’ll reimburse me via personal check after I ship it back to him. What should I do?