They have telemetry. They probably know when a game is downloaded. They probably don’t know if it’s legitimate. They just auto bill based on telemetry and leave devs to dispute or suck the big one. Only effort needs to go into disputes. Big clients will obviously get quicker resolution.
No company would trust devs to be honest about downloads and it would be too expensive to verify.
They don’t need to audit much, just need a steam, epic, and itch total downloads figures.