Most of the shops make significant profit on sales of parts. This is one of the reasons why they don’t like you to bring your own parts (but not the only one reason!). There is nothing wrong about this, actually it is a good thing for customer as profit made on sales of parts helps to subsidize lower labor rates. If shop would not make profit on parts it would have no choice but only close the doors or increase labor rates (that are already high). When shop encounters electrical repairs or complex diagnostic job there might be very little or no sale of parts at all (technician found a broken wire and soldered it – what is it to sell here in terms of parts but a blob of solder and a piece of heat shrink insulation?). This is the reason (again, one of the reasons) why some shops apply higher hourly rate for diagnostics.