Learn to use /follow and /m
/follow <offending player>
the suspicious person... search youtube for tremulous aimbot or tremulous wallhack to see how it looks to the player and how they act. If this looks to be the case, then PM an admin on the server (ask who's the admin if you don't know):
/m <admin_name> yo mr. admin, spec <offending player>, he's aimbotting, I just speced him and saw it.
If they aren't botting, then continue to watch them, and learn from them / also learn how to counter their tactics, look for weak points in their methods.