They replaced the 2 outside sensors first as a test. They got lucky on there first try as it was one or both of the outside sensors. They are a good dealer ,yes. Another option for you if you can do it your self is to buy a new sensor on your own . All four are the same part #. Start to replace one at a time . In other words puy a new one in one position and try it for a few days and see if it beeps any more. I f beeping continue substitute new sensor to the next spot and so on, Finally when you find the bad sensor contact dealer have them reimburse you for the part and have it painted. The sensors are inexpensive. in order to access them you would have to remove cover partially
to access them. To short the time you could buy a couple of sensors.