Checking for rust … common areas?

Unless you know and trust the seller VERY well, do not rely on their description of rust. Even well meaning people will lead you far astray.

I agree with 1968. Find something close and look carefully yourself. If you don't know how to look, find someone to go with you. Only rare cars are worth going long distance for. Look through restoration threads here and you'll see loads of pics of rust. The floor pans are not the biggest concern. Frame elements and quarter panels are much more important.