Our is also kept very clean.
Outside is washed every 3-4 weeks depending on weather and waxed a few times a year.
Inside: we never leave stuff in the car when we are not in it (other than the few things which truly belong there: first aid kit in the trunk wheel well, car charger in one of the slots that would be an ash tray in a car with the smoking package, owner's manual, coupons (non expired), "emergency" granola bar, and napkins in the glove box).
We do eat in the car, but not tons and we are careful about crumbs so they do not get bad between vacuuming. DS's spot is the worst, meaning it can be noticeable.
In good weather it gets vacuumed a couple of times a month but it can go 2-3 months in between in the heart of winter.
also in good weather we lotion the seats, clean the dash, etc at least once a month.
DH's coworkers are always trying to figure out how it is that he is the only one of them with kids and yet he has the cleanest car
