EDITED
Andy, as you can see there are differences of opinion. Mostly because we can't inspect it. I don't think I see anything bad. It's for you to decide after you inspect. My opinion on this is: re: rust:
1. If the floors, foot well and steps are OK. If there are is no 1" think bondo repairs

2. If the frame is OK
3. If windshield surround is OK
4. If you can DIY
5. The cab corners and doors are a standard repair with available inexpensive patch panels.
6. I don't see any other rust-out/rot-out..yet
7. It is a little high priced. if it has been offered for a while and if you ask the owner "is there any room on the price?" If yes, Then go see. Those are the exact words. Don't offer a price until you see it. Then inspect and offer what you think. I can see you know about trucks so you are not a rookie. Our opinions are NOT near useful from pictures. There is a lot to be said, as Martin said, about regional prices and availability. Shipping right now is VERY high and an immediate loss for the buyer.
No one here can see major rust. Structural damage, Need for new cab or anything wrong with a steel bed or temporary plywood bed. They are speculating and advising where to look for problems. You are not going to find a 100% stock truck without rust unless in the "restored" price range.