Black Ops 2 - Safe to buy used?

Hey guys, hoping you can help me out here. Work network blocks forums related to game playing, so I can't get an answer on my own.

I have an X360 and I want to play black ops 2 zombies with my brother.
Is it safe to buy a used copy, or do I have to worry about the previous user "using up" a key to activate multiplayer?

 

id but i got it msg me if interested disc in great shape for 360

 

I ended up getting a used disc that night before I saw your response.
In all though, things worked great, saved $30 over new. Of course later my brother tells me, "now you need all the DLC". Freaking $60 more, lol.