The only exception to what Hamma said is enemy equipment/vehicles.
If a NC has the medium assault cert (the assault rifles), and he comes across a TR cycler, he has something that he (and his allies) can use, but cannot easily come by. The ammo is in plentiful supply (standard bullets), but not the weapon itself. Ditto the other way around, and the jackhammer uses standard shotgun shells... so anyone with a flechet rifle cert can get ammo for it.
I don't think there will be a trading system though... because these situations aren't that common.
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