need help to fig out value of a 1972 duster

It is really hard to deal long distance with the pictures shown. The car appears to be nice(well at least ok) 6k is not out of line, however a lot of problems arise when the seller doesn't want to assist a long distance buyer with detailed pictures-- undercarriage, floor pans, etc--- all the things you will look at when inspecting closely..
He might think he is giving the car away now-- or he could be a salesman hoping to hook you.

If you really like the car-- get the details from him with pictures or travel there to inspect. Lawrence