Check to make sure the front sight is not canted either. I'm not sure if you're talking about a SAR-1 or a WASR-10 (which is what I have). But also see if the magazine wobbles excessively (doesn't affect functionality but I don't like it).
Finally, check this thread:
What would one look for if they decided to buy an AK? - M4Carbine.net Forums
Good info.