I have been well aware over the years of dealers adding things like screen wash top up to a service, even when not needed, so I always make sure its topped up before. Recently I had an annual service at a Mazda main dealer and saw they charged for screen wash, I question this as it didn't need it and they said it was a bottle of it left in the car. As I needed some and it was a similar price to what I would pay I took it. I know margins on selling cars are low so they try and sell you many needless extras, are margins on services small too so they sell you something not asked for that costs them 5 times less than they charge you?