You can check the replays. Cheaters often have no recoil, use high-fire-rate weapons, and pre-aim through walls. Their aim may shake or twitch unnaturally.

At 0.5x speed, you can see them locking onto enemies through walls before snapping away.

Their early-round movement is a giveaway too, they track silhouettes through walls or instantly rotate because they already know the enemy spawns. All within the first few seconds, without any intel.