Fine tuning this one a bit more.
Player A drives into the car wash because they just did some off-roading and would like their vehicle cleaned. Player B is working the freelance job for the car wash employee. Player B tells Player A where to drive up to. Player A gets out of the vehicle and Player A naviagtes a WI menu to request the car wash and pay for the wash, Player A inputs the license plate of the vehicle they are requesting. Player B gets the notification and has to complete several tasks for the car wash to go through. Once done, Player A can drive out and enjoy their fresh-looking car.
Payment would be uniform and based on the car TYPE. Sedans and compacts would be relatively cheap, sports cars and super cars should be a bit more expensive (not 20k expensive but a bit more)
Obviously, I know nothing about development and programming so take this with a grain of salt.