Rust inside exhaust silencer

Some poephol from Kloof, KZN sold me a "brand new" KTM 2017 silencer which he promised comes of a new bike and the bike probably hasn't been fired up with it. I trusted his bikers honour but when I received it, I noticed it was definitely used by the dirt stains and marks on the outer bottom and the canister is rusted inside.  I can live with the fact that it was used and dirty, but is it safe to use it with the rust inside or do I need to have it refurbished or rather buy a new one from KTM? Mine scratched on the outside and wants my 2018 KTM250 to look like new again.