How do I determine if someone is cheating in Call of Duty: Black Ops?

I've played games with some friends and they claimed that so-and-so was cheating. I honestly just thought that he was a really good player.

What are some indications that someone is actually cheating?

It is very hard to tell nowadays, where you can rack up kills on tight maps like NukeTown by using Hardline and getting a mass destruction weapon like the Gunship or the Chopper Gunner.

Speed hacks (he moves much faster than anyone ever can) and health cheats (he just does not die) are more obvious, so I am not going to mention them

Wall hacking is the most commonly used type of cheat where one can see through walls and track enemies from very far distances.

Some indications are:

1. He has a ridiculously high kill-death-ratio. Especially when deaths are less than five.
2. He plays with a sniper rifle the whole time, and can kill from the other end of the map before you see him.
3. He is prematurely firing before you actually show yourself around corners.
4. Shoots through walls/doors where you know it's impossible to detect you there.

There are some caveats to the last one, though. He might know you're there because:

• There is a spy plane in the air and you don't have Ghost.
• There is an SR71 in the air (Ghost Pro won't protect you here).
• He has a motion sensor installed in your proximity (Ghost Pro won't protect you here, either. Only Hacker Pro makes you invisible to motion sensors).
• He has previously thrown in a nade (flash/nade) and saw it "connected" someone and he tried his chance by spraying in the possible places (it's obvious a lot of people camp the wooden rooms and the caravan wagon on the map Firing Range)
• He has Ninja Pro and heard your footsteps from further away.
• He is on a lucky day.

There is one test to almost exactly tell if he can see through walls: the step-ahead-step-back technique, in which you need to know the place the player in question is before hand. As you are coming out of a closed space or round a corner, just run to the corner and before you really show yourself, back up a step. If he fired before you appeared chances are high he was tracking you through the walls.

As you can see, finding out whether someone is cheating is not an easy task. He might just be a good player, having a strong intuition or excellent knowledge of the map, and a good timing. I would really not take this as a rule set to say yes or no, but as a checklist of questions you ask yourself before accusing someone.

For sake of completeness, check out Toastandjam18's interesting answer below about boosting.

Some clear indicators are:

• On kill cam he "jumps" from target to target always aiming to the exact same part of the body. (The majority of the time being the head.)
• He automatically shoots in predictive manner or immediately after aiming.

What must not be confused as cheating:

• Randomly shooting at common camping places. (Pros can also headshot)