I was up early and bored, so I sent the guys this note:
A couple of problems with your ad-
1) You need to make an effort to try to find its owner - maybe you already have. Try www.mountainbuzz.com and post in the Lost and Found forum. You can also contact Jackson Kayaks in Jackson Hole, find the serial number printed on the boat, and see if they have a registration contact on file. Their number is 931-738-2628, and they can tell you where to find the ID code.
2) That hull is severely compromised from that dent, and it isn't safe. And it's not worth $400 either - most boaters will know that. But someone that doesn't know what they're buying might themselves pinned inside it because they are aware that the hull is at a much greater risk of collapsing under pressure.
And he sent me back this:
thanks for the help. Much more of an effort has happened than you realize to try and find the owner. Thanks for the inquiry. And about the hull, Jackson will warranty the hull and since it is this years boat they will receive a new one for free. It is worth at least 400 because of that. Thanks for the inquiry.
So maybe he's not a dick - probably just doesn't know how to find the owner and gave up. I wonder about his faith that Jackson will warranty the boat, though - Great company; but that thing obviously went for a user-error ride.