Excuse me, do I need to return the car clean or just with a full tank of gas? The car is not very dirty after we used it ?

As long as it's not too dirty, it can be okay without washing. As long as there's no smell of cigarettes, it's fine.

Just fill up the oil, unless there are coffee or fruit marks inside the car.

Mainly the interior must be clean, no strange smell, the exterior only needs to be able to pass the car dealership inspection.

Washing is required and the car must be returned with full oil. There are simple car wash brushes at the gas station. There are small buckets, so you can wash it by yourself. I simply washed my car after filling up with gas before returning it in Sydney, which didn't take much time. Don't fill up in the city center, it's too expensive. Try to fill up in the suburbs. I haven't filled up in Bulimba, I picked up the car there. Then I filled up with full oil in the suburbs of North Sydney and drove about 20 kilometers to downtown to return the car, and the fuel gauge was full. 95 octane is an average of 147. Also take a photo of the mileage gauge when returning the car.

As long as it's not too dirty!