There seems to be a lot of misinformation in this thread. First, I would not assume that the car has had prior rework. I'm not sure why people are saying that, other than to just make the OP feel bad about an already frustrating situation or to feel better about themselves. Yes, cars can be damaged during delivery, at the port, or even in the factory. Typically these are repaired using techniques and materials equivalent to the original production. Said another way, the repair is virtually indistinguishable from original, and of equivalent quality as the original (not worse). So I'd be interested in knowing how someone can look at a somewhat grainy photo of a door after the paint and seam sealer have been scraped off, and so confidently assume it's been repainted.
Second, in practical terms, there's no such thing as rust proof steel -- sorry, but that's just an euphemism or poor writing. The correct term is corrosion resistant steel. All steel will eventually rust in real world usage. The purpose of galvanization is to extend the majority of corrosion beyond the useful life of the car. But that doesn't mean the car is impervious to corrosion. Further, at a microscopic level, there's no such thing as a car being truly "rust free", even when brand new. The surface of steel contains pores, and other microscopic crevices. Fresh uncoated steel will corrode at a microscopic level when exposed to humidity. The steel is cleaned before stamping and galvanization/primer/paint to try and remove this. Sometimes, corrosion in these small crevices is missed, and over time it can grow. Sometimes, the cleaning job is subpar. The galvanization process can help with that. But, galvanization isn't perfect either. It's a sacrificial coating (anode), and will slowly sacrifice itself to save the underlying steel (cathode). Further, if the door was hot-dipped galvanized at the factory as a finished subassembly, then the galvanization may not penetrate well into the seam. This where the seam sealer is supposed to help lock out humdity and salt to inhibit corrosion. However, if the steel wasn't perfectly clean, corrosion may grow inside the seam over time.
FWIW, I had a 2012 Mazda3 that developed rust from one of the spot welds on the interior portion of the door frame. It was very clear that rust was developing from inside the weld joint. I think Mazda has gotten better on their rust protection, but I personally think they still have some catching up to do.
