I think the OP hit the nail on the head in regards to the sales side. Its all about relationships. We all should build one with a good service advisor. I've been told that they get paid on commission. If true, we need to stick to the good ones, weed the idiots out.
I'll give you an example. I had a clicking from the right rear on my 330 when I would compress the suspension in park or forget the take off the ebrake in reverse. I took it in, had it looked at. The advisor said it was my aftermarket wheel, they cleaned the hub and charged me $200. Ended up being normal function when the ebrake was engaged. This same advisor would only change out one coil pack at a time accordind to the engine fault code despite there being a recall for all of the coil packs.
The one I have now replaced a rear brake pad sensor...CLEARLY it was not a warranty issue. I taped up the sensor at the track (too lazy to get a zip tie), came loose and it got eaten up. I actually forgot I spliced the wires together when I took it in for a brake service. He replaced it under warranty.
2015 F34 328iX GT Glacier Silver
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red