The cleanliness of the car while you're using it is your responsibility. Each renter is expected to return the car in the same condition as it was when they picked it up. I try hard to make sure it's clean when you get the car, that way you only have to clean your own mess if you make any. Pictures of the inside are always included in the check-in photos.
Messes to clean up before return the car include crumbs, sugar stains, any other type of stain, dirt, napkins, documents, wrappers, and litter.
A handheld vacuum cleaner and wipes will usually be provided as an option if you want to clean things yourself upon return, otherwise a car wash is available nearby as well.
No pets, no smoking, and no overly feathery scarves please.