Buying a used rear end what should I look at to see if it's in good condition????

Hey yea it's a a body rear 741 case , positraction and aftermarket 3.54 gear ring and pinion . Also sorry it's just the third member . Reason i was asking I only see them going for a lot more like 800$ in my area. This sounds like a good deal to me . But I don't wanna go and buy and busted third member haha . That's why I was wondering if there is certain things I could look at to see if it's I ln good shape .