I've done that twice with some shops I didn't have any history with.

Once I got them to replace my gearbox oil even though they said it wasn't needed. With another one I brought them a third-party pedal and asked them to install it. In both cases it did solve my issue by the way, even though I might have been wrong.

They don't care as long as you're ok to pay for the hours regardless of whether it solves your problem or not.