need help to fig out value of a 1972 duster

All the before mentioned is stuff you need to ask before looking, better yet would be to have him send pics of the VIN and fender tag. If you do go and look at it look for a washer welded to the front edge of the k-frame, 340 cars all seemed to have this. Keep in mind that if it is a real 340 car that the rare and expensive sharktooth grille is missing. If the VIN # checks out you can always pull the rear seat and look for a build sheet.

Car looks pretty good on the outside, make sure to crawl under and look at the frames and floors, also areas in the cowl and inner fenders where rust is common too. If he don't know squat about the engine he probably doesn't know what body work was done.

I would say as it sits, if it is clean and solid and a real h-code car, maybe $5-6k? Need to know lots more about it like condition of the interior, what front brakes, does it have an 8 3/4 rear, rebuilt parts like trans or suspension. Maybe the seller can take more pics for you, he must atleast know how to use a camera!