Personally, the only work a dealer would ever do to my vehicle is warrantied work with no out of pocket. Or a recall.
Otherwise I depend solely on word of mouth close connected friends. "So and so who owns a VW shop referred me to you". I do most of my own work outside of major major stuff. If I can do it over a weekend and avoid the whole dropoff pickup no car for half a week thing, I'll do it.
Biggest minor scam we came across was I didn't have time to get car inspected one year so wife took it. She called me about it failing for a tail light out. The shop wanted to charger her like $110 to take 30 seconds to put in a $5 bulb. They tried to play the "book hours" game with me on the phone and I replied "so you can honestly say the book says an hour for the 30 seconds to open the flap and change it?". I came and picked it up, drove to Autozone, and was back with the bulb installed in 5min. I made a scene in the lobby in front of their customers about trying to take advantage of a woman who didn't know how these things work.