Sounds like a parts donor car, not a driver. As such the only way to realise its full value (which might be close to 4 grand, not 6, from the info stated) is to part it out. You cant expect someone who is going to consume the space and spend the time and money towing and stripping it to pay dollar for dollar what the car is worth to part.
Offer 1500, see if he starts to negotiate his price. If he doesn't, slap him a high five and walk away. Do this in person. Don't overpay for a shit old car.