Wow - I've never heard of that mildew removal process before. I'm very impressed!

As far as the strings, they were listed as "new," which means they shouldn't be rusty - so the seller is required to take them back regardless of "as is" provisions. Accurate descriptions are helpful. I've generally had good luck with getting items that were not as described returned or discounted (these would have to be returned), generally by being very polite, assuming the best of the seller (ie, they would never have knowingly shipped something defective) and asking them how they'd like to proceed. Only one have I had to make an actual complaint, and that was for someone who never shipped the item and dropped off the face of the earth.

I wouldn't buy strings on Ebay, as a general rule, though I have bought a couple instruments that way. They're probably there because they'd been sitting around somewhere for too long, and are now being liquidated (to the point of rust, apparently!). A trustworthy online source like Elderly or a local store you can hold accountable is a much better bet.

Dan