What would you pay for this 1974 340 Duster?

I'd be most concerned about what all was done to the engine to handle the extra HP. Which casting heads? Steel crank? Fully balanced? Etc. If it just has a supercharger bolted to a stock, cast crank, '73 engine, that won't last. Is that headliner just vinyl glued to the roof? Lots kind lumpy for cardboard. That cheesy steering wheel would have to go. They need to find the correct glove box door/bezel to finish off the dash. Looks like they're asking under 15K but how much under? If you like the car and it's sound, make him an offer and see.