1) it's a very
valuable stamp, if genuine. If you didn't pay close to market (in the thousands), it may very well not be the real deal. If you inherited
it, you might be very lucky, indeed.
2) forgeries of old Swiss issues can be very, very good. Doubtful you'd be able to tell yourself, or to apply any advice we offer, with accuracy.
3) Why on earth would you be hesitant to have a such a specimen assessed/certified by experts? You'd certainly never be able to resell as a legitimate issue without a cert.