Trial and error diagnosis by BMW Auto Alpine

Took my BMW 335 for repairs - intermittent squealing noise. Was told that it was the starter and would cost circa R15K. The starter was replaced but the noise came back. Took the car back and was told that the fault is in the engine and would cost another R9K. No responsibility for the mis diagnosis. Dismissive. Either gross incompetence or management that simply does not care or profits from double work. Lets see how they respond...