well make a good guess about him/her
1. check his level
2. check his HS % (that usually tells you alot since telekill aims at head for most part)
3. play a game with him/her, people chamming are obvious for the most part, same with aimbot
4. check his cbl/nexon profile (see if he actually ever used nx weapons, if he claims to have)
5. ask for video proof, so just tell him to record this game and upload to youtube. most hackers just QQ and make up silly excuses. If anyone asks me I record it and upload to youtube saved as their name XD
6. ask for TV, most hackers react same way as #5.
All these steps aren't necessary, but just something to help.
I never saw a aimbot that worked with fireteam. :S