[JFP in PA]

Asking a shop to forgo the margin that they normally earn on a given project (parts & labor) is inappropriate for the reasons already mentioned. Many shops set their target margins on a given project, say a clutch replacement; and when asked to install customer supplied components, they do two things: They get a "hold harmless" release from any liability if the parts are wrong or defective, and secondly they charge you an amount equivalent to that expected margin they would have made, so you still end up paying them what you would have done if they supplied the parts. There is no such thing as a free lunch, and if there was, you wouldn't have time to eat it.