General maintenance and servicing is the responsibility of the host.
The host must ensure that servicing is done a few weeks/months before the car is given for rent for a long term.
If the car is due for servicing then the guest will not be charged for the days the car is at the workshop.
If the car needs to be serviced due to actions of the guest, then the guest will be charged for the days the car is at the workshop.
The general principle is whoever is responsible bears the cost.