Kevin is right. The photos on the craigslist entry clearly shows a "dorm fridge" installed where the 2-way refrigerator should be.
The AC unit that's installed appears to be the original Armstrong. The one on my '75 works great, though it's a bit noisy. The furnace isn't mentioned, so I would assume it's the original one. That essentially means it's ready to be replaced. Ask lots of questions and verify as many of the answers as possible.
Argosy trailers have the same basic qualities as Airstreams. When evaluating one from the 70s check for soft spots in the floor, especially near the front and rear of the trailer and around the door, refrigerator and wheel wells. Find out if the electrical system has been modernized or is still using the original Univolt converter-charger that's hard on batteries.
Definitely take Kevin's advice about using the Trailer Inspector's Checklist
. Also, if you want to try to find someone experienced to look at it, you might consider contacting some volunteer inspectors in the area near the trailer to help you inspect it in detail.