It's not just BMW. 15 years ago, I put front brakes on then-wife's friend's Saturn.
She had been quoted by Sears @ $450 for front brakes, and when I caught wind of that I told sent word out that I'd take care of it for her.
She cancelled her appointment a few hours before she was scheduled to show up.
She brings her car by my place, and I go to Autozone to buy brake parts (pads and rotors).
Pads are pads, but the first kicker is this: On one of the rotor boxes was written in Sharpie "Sears, 6:00P"
6:00PM was exactly the time that her appointment was for.
These therefore are exactly, precisely, and uniquely the same rotors that Sears was going to install.
So here I am, installing ~$80 worth of rotors and $notmuch of pads, as an unskilled tool in a stone driveway on a cold night when I was already going to be working on cars anyway.
The only difficulty was that I needed some big Torx drivers that I didn't yet own, so went back to Autozone and got a set of those.
She paid for the parts, I ate the expense on the tools and donated the labor, and everything was golden...
until she elected to order pizza for everyone in the house (including the kids that she brought along) and then insisted that I pay for half of that pizza order.
She even had the audacity to hit my wife up for pizza money a couple of weeks later.
No good deed goes unpunished, I guess. I did a fine job on her brakes and it wasn't any particular challenge (and a "real" mechanic would have had the big Torx driver to begin with), but I guess the lessons are two-fold here:
1: They saw her coming, and inflated the rate to take her for everything she could give.
2: She saw me coming, and decided to take everything she could from me.
In the end: Then-wife stopped being friends with this lady soon thereafter, and I never saw her again myself.
But the point is: Bad mechanics that like to take advantage of folks do exist. They take advantage of everyone they can. But they particularly take advantage of BMW owners, and I have my own horror stories about that which I can relay upon request.
(But in synopsis, it usually, it goes something like this: "Wow, that's a lot of money." And then they reply "OF COURSE it's a lot of money! It's a BEE EMM DOUBLE-YOOO!"
But it's just a car, not much unlike any other. And excellent parts are very inexpensive if bought properly, even if it is a BEE EMM DOUBLE-YOOO!)