Unless the weird smells come from the driver. If a customer causes a smell the car will be cleaned and the customer fined. If the driver is smelly - like from sitting in a car all day - there's nothing to be done.
Who can tell who caused the bad smell? If you have a driver they'd know but how will Waymo know which of the 20 or so riders dragged in dog doo, maybe the doggy doo accumulated through the first 10 rides. Who foots the bill then?