How do you figure? It has the 72+ rear side markers, indicating that the shell is at least a 72+ car. The doors are 73+, they have the plastic tops. And you can’t see the VIN in any of the pictures. The front end is definitely ‘71. Nothing in the pictures to indicate it isn’t a ‘75 Duster with a front clip and tail panel swap. Tail panels are pretty easy to change out.
Now, that said the car is way overpriced for what it is. It should be priced like a ‘75 Duster, and in that condition it’s not worth half what he’s asking. And I would definitely check all the numbers on it to make sure nothing really funny went on with all that part swapping. If it’s legit all the numbers will be for a ‘75 Duster.