Well, to start things off, they are not modding.
This is coming from a black ops player who has literary gone over 100 kills in a single match.
Ill answer your questions in order-
1- People often get angry when you ask them if they are hacking (most laugh too) But honestly, if they are going 50-0 then they will believe they are superior to you.
2- People ARE skilled enough to know where you are. there are three ways to counter this. 1. use silenced weaponry 2. always use ghost pro 3. know the layout of the map!!! i cannot stress this enough, you will see a drastic improvement in your kill-death ratio if you know your way around the map.
3-Usually mods are much less subtle than you think, if someone has an amazing killstreak, they are just good. if the kill feed is actually only headshots from the same guy, its probobly a mod.
4-there are no admins in black ops, they are simply high level, and they cannot ban you. the only way to be kicked from a game is if you team-kill.
Now here is how to improve-
1. like i said before, KNOW THE MAPS!
2. watch gameplay videos on youtube, you will find your gameplay will improve if you have more tips from pros (like me) ;)
3. play more in general, and get a feel for the controls. practice makes perfect.
I hope you find your kill death ratio improves!
-kctellie