The 71 body appears clean. Some orange? showing through in the primed areas.
Many Challengers usually rust out on the bottom of the front fenders, and lower quarters in the rear as typical.
Trunk floors are usually gone, and cars with vinyl roofs have trouble in the roof or window trim areas.
Cowl areas can also be a hidden problem.
I know that we can't see every thing on this car, but the body visually appears decent without the typical bottom of fender/rear quarter rust.
The bottom of the passenger door could have been primed due to rust spots as well as the rear quarter louvers where holes are drilled for installation?
Who knows without a direct inspection. Looks like a fun RT survivor to me; I would take it home.
Just my thoughts!