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I can't see any rust holes in that pic, also its not the place to check for rust in a C3, you have to pull out both kick panels and check the bird cage bases, and also to remove the A pillar plastic molding and check the windshield frame corners, these two places are the most common to have a bird cage rust.
if it is that bad at that point in the bird cage then I would hate to see what the windshield frame is like further up. Pull the inner kick panels and see if you can see the body mounts. I bet they are completely covered up by flakes of rust debris. You should also check the integrity of the frame especially behind and below the door just before the frame kicks up before the rear wheels.
From what I see there you should have the car professionally inspected by someone knowledgeable of a C3. By looking at those pics... that is probably just the tip of the iceberg.
Someone has sealed up the space between the upper fender and the hinge post with some kind of body caulking /sealer. That should be open what lurks behind that could be a real issue. The windshield frame (“pinch wield) itself is a job to repair but very do able. The lower corners that are behind what is shown in your photograph and the hinge post are major jobs to repair. That can mean removing the entire front clip and even the firewall to repair properly. You would probably want to make sure that car does not have these issues before buying it.