because the people your playing with are probs the cheating modders which ruin the online in GTA4
well eventually i managed to doge their bullets and atatcks for soo long they thought i was modding XD theyd get in car with me and let me take em random places XD
Only a small percentage of people actually mod.
After you press the left trigger to aim, press in on the right thumb-stick to zoom in, then use the right trigger to aim for their head. Also make sure to tap the trigger quickly instead of just holding it down for better accuracy.
He's a silver account...? Oh well, since you're using a 48 hour you won't be able to experience that again after them hours are up.