IMO if they're good friends they won't ask for or expect a free car wash. If I go to a friend's wash I expect to pay, but I'll take a free one if it's offered.
I've had a lot of people hang around the wash acting like they're someone I've known for years. I used to give friendly people the occasional freebie, then I couldn't get rid of them. If I never do, they stop coming around. Some friend, right?
Close family is free, siblings, parents, aunts and uncles, cousins only if we grew up as close as siblings. Relatives I only see when their car is dirty should at least act like they expect to pay. Luckily no one from my mother's side of the family is like that, and I never see anyone from dad's side.