I think there's just too much there that isn't from a 70, and buyers are maybe cautious because of that. What Im referring to include the rear fender/light, seat, headlight ears and probably light bucket, rear turn signals, triple tree, gauges... makes me think that even though the serial numbers of the frame and engine can be from a 70, a lot of the bike may not be.
No offense meant, just giving my opinion based on what I see. Good luck with your sale just the same.