Salt damage / rust on used car?

I'm interested in buying a used 2006 Honda Civic Si. However the car is from a snow state and I have heard about the damage the salt they use in snow states can cause to a car. However I didn't see any rust on the undercarriage or anywhere except for the rotors. The car has been out of snow for at least one year and it was only in Oklahoma for 5 years. Is this even enough time to cause any worry? Does the rust on the rotors mean that there could be later issues? Everything else looks clean including the paint. I'm worried that this car may turn out to cost me more money than it should.
Anyone have experience with this sort of issue or recommendations.

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