It all depends upon the deal (including how much you are interested).
Restoring this bike is not a problem these days. Genuine, used, Chinese parts are now available easily in Karachi.
I have been also interested in older models just like you but short on funds right now, rebuilding my car these days.
Anyhow, I will go for such models if following areas are not doubtful,
Frame is not accidental (if accidental, simply back out of the deal).
Engine/Head. (Though no one can make sure how much life is remained so I would be expecting engine rebuild cost in near future).
3. Wiring. I would check components (like CDI, Charger, Self start system...etc) if they are genuine and working. If they are Chinese, altered, altered wiring, then make a deal against it. This electrical aspect especially in GS is very crucial and repairing can become very very expensive and a nightmare for the owner. A MUST THING TO CHECK !!!!! ALERTTTTTTT !!!!!!
Rest is not that much critical but you can bargain upon the given condition of the bike.