Right and the other part is how do you know when the footage needs to be reviewed?
Just add two buttons to the app "minor cleanliness issue" and "major cleanliness issue". Then someone remotely checks the footage. If it is confirmed then the previous passenger gets charged a cleaning fee. Majors cost more or could result in ban. Cleaning can be done by carwashes.
Eventually you develop some clever covers and devices/stations that enable rapid cleaning.