If it is a Yugo, (grenade laucher, blade bayonet still mounted), AND shows obvious wear, say no. The "shooter" grade Yugos can have burnt gas valves, corroded bores, etc, from years of being shot with corrosive ammo in Yugoslavia. They also have unchromed barrels, due to no natural chromium deposits in Yugoslavia, which means corrosive ammo worked faster at destroying the barrels and gas systems.
If it's a Yugo with very little wear or damage, (there will always be some handling/storage dings), then start checking it out. The "unissued/excellent" condition yugos are really quite neat! I have two, and they work perfectly.
Ditto on getting ALL the cosmo out, including the bolt and gas system. PITA, but very very necessary!