Alright lets get it started.
Your problem is with lag,hacker,etc right?
1.Well if its a hacker they can shoot through walls with out notice.
2. it can be because of lag like 500ping (Max) you will start to see that you are shooting them a million times but you die and the other person doesn't die. Its probly some thing to do with fps lag. Laggers=goes through walls.
3. It could be the host who is controlling the kill (Host=power) but im pretty not sure tho.
Hope this helps!