You have to take photos of it right away, "proving" the passenger's "damage" to your car, submit a ticket to the support team with said evidence, and if you're lucky they'll reimburse you whatever it cost was incurred to get it cleaned (with proof of that as well), and nothing more. You don't get to just name a price. 

They're bastards about this, I had some drunk, er... ladies... who were secretly drinking white wine in my backseat and not only spilled it, but then left the bottle dripping in my trunk. I was unable to get anything out of it.