I know you're really talking about the state of the interior in general but with regard to smoke they could be fitted with immobilising smoke alarms. If the sm

I know you're really talking about the state of the interior in general but with regard to smoke they could be fitted with immobilising smoke alarms. If the smoke alarm goes off the car pulls over and stops at the side of the road. The rental company will already knows who in the car at any one time (or at least who has rented it) and they can just issue a massive cleaning fine. Like setting off an airline toilet smoke detector.