[wayner]

As an impartial bystander, the car does not look rust free.

Almost rust free would be a better description, especially since it is rusted in a common area for these cars.

For reference, I once went to buy a car that was "rust free" When I reached underneath and a chunk of frame rail came off in my hand and the car looked structurally unsound, the seller said, "that's just surface rust."

On the part of the seller, I would be careful with the use of those words.

On the part of the buyer I wold be careful relying on an assertion without seeing evidence.

Given that, I would say it is an understandable misunderstanding by both buyer and seller.