Let me guess your here to cry about hacks.
First of all, did I/my team have UAV up, or did I maybe just use a killstreak/equipment/specialist which made me able to see or hear your location? Most folks don´t have a memory longer than a ♥♥♥♥♥♥♥♥ goldfish. Then over to the important part, SOUNDS! Near 300€ on headset and soundcard. Remember that you also make sounds when you climb over an obstacle, jump, reload and activate killstreaks. And let's never forget grass and snow, it's really easy to hear you move in it.

Now enough about sounds, with sad lot of experience which i have it's easy to anticipate where people go, what they're going to do and how to counter it. Memory has already been mentioned regarding killstreaks, but seriously, it's not hard to remember where you were camping when you killed me one kill ago. And let's not forget coincidences, don't mindlessly accuse someone the first round because the killcam seemed weird. Pay very close attention to killcams, alot can happen in those brief 3 seconds.

Friends in party are also useful resource to have and they can inform where the enemy is and from where they got killed. Don´t always asume that people that are better than you are cheating.

Oh and if it's aimbot, not wallhack, you're accusing me of, you clearly have no ♥♥♥♥♥♥♥ clue what aim is.

Remember, it is OK for others to be better than you.
Oh if your still crying please leave a comment below I still like to laugh.