I'd return it and not buy anymore guns without seeing them, unless it's from a reputable vendor.
The rust may be removeable with a lot of work, but at $200 you paid for a clean rifle in good shape.
Mine was a perfect '54 Tula for $180. Russian SKS's were chrome lined after 1951, approximately, btw.
That's a perfect example of shooting corrosive and not cleaning thoroughly when you get home.
I'm too busy at times to be bothered with that, I shoot non corrosive and clean it within a day or two...I also
did the Sailor Curt Youtube mod on the trigger to make it sweet, put iridium sights on it, and polished it, so
I don't want to shoot that corrosive garbage through mine. Hope it works out for you.