63 valiant

I would check the compression. Best to use a screw-in gage, but in a pinch you can turn over the engine by hand and feel for each cylinder. If you hear each one slowly hissing down (>3 sec), the engine is sound. If so, I wouldn't worry too much since you can fix the poor running problem. Sounds like the carburetor. I wouldn't even fool with the points and go straight to electronic ignition.

In this case, the engine dying would be a benefit since most others would walk away from the car, so you can negotiate a good price. Don't feel guilty. If the seller was motivated they would fix it before trying to sell it. By not doing so, they are admitting "whatever I can get is fine".