Need a better picture of that For Sale Sign !!! LOL
Start it and look at the Harmonic Balancer and see if it is wobbling or If it spinning true.
If it does not do it at idle and only in gear,have a friend power brake it and look at that balancer....
I would definitely use that vibration as a tool to lower that price!!!
That one clean Dart,
Good Luck,
TXDart