Sorry to hear of your unfortunate experience. I drive 22 miles to a dealer i feel comfortable with as opposed to one that is 6 miles away that i have heard "stories" about. Piece of mind is important and trust is a big piece of that. I drilled heavily into the 4 yr/50 kmile aspect before buying as I got my vehicle as a service loner with 6100 miles on the clock. Though it might have angered the service person, I checked to make sure that i got the Castrol SLX oil going into my vehicle. All has been good and I am doing in between oil changes myself. To each his own as this topic has a many varied opinions. I actually have found buying the oil at the dealer is the cheapest.
My dealer was even nice enough to let me get some of the old oil as it came out of the drain plug for oil analysis. I feel they understand of our carefulness since our D's are unique and require special care. Good luck on finding a good service dept.