I have fun with some of my laundromat customers trying to shame them into also using our car wash. Sometimes it works ... sometimes they are offended ... sometimes their excuse is "it will just get dirty again anyway!"
As far as messy ... I don't know if anyone else has seen some (not all) living out of their vehicle drivers ... but I have. Their pickup with a topper or their car can be packed to the gills with anything & everything with no room for even one passenger. I tend to not say anything to those drivers because like a "scaredy cat" I know that they can also be a bit on the "volatile" side.