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I haven't even seen the frame or the advert and don't know what you paid, so take my opinion with a pinch of salt.
But from what you wrote, I don't think you've been hard done by.
A bit of Emery cloth will clean the steerer up and there are steel frames three times the age of yours still doing good service.
I appreciate you're disappointed, but both sellers and buyers are naturally inclined towards being optimistic about a trade, so it's rare that neither are disappointed.
Unless it's rusted to fuck, that's not what's rattling around inside the tubes.
Surface rust on the steerer of ~20 year old forks? Well... yeah.
I don't mean to have too much of a dig, but you're not being realistic.
Imagine the flip-side posted on here: "I sold a 20 year old frame and the buyer is moaning that there's some surface rust."