B.S. I've had several CO, UT and NM trucks that were just as clean as anything from AZ which I've also have owned. Out of the over 40 Western 72-80 trucks that I've owned none had any rust in the roofs. Totally an East side thing. Floors and above the rear wheel wells and lower corners of the doors are the rust issues out here.
This 77 Macho came out of NM about 6 years ago. Paid 2500 for it. 360/727. It did need two quarter size rust spots in the door corners and a couple in the roll bar fixed That was it. Put a bunch of money and hours into it and then it eventually sold for 28,000 which is probably the top of the spectrum.