I had a rework today for brake noise. How do I distinguish between an installation issue and a break-in issue?

A car came back two days after I replaced the pads and rotors, with the customer complaining about a squealing noise at low speeds. The biggest fear with rework orders is redoing the job for free right away, so I first test-drove the car to confirm the conditions under which the noise occurs, then checked the rotor surface, pad bedding, caliper slide pins, and the clearance of the backing plate…