Yeah…it wasn’t my car but I was watching a tech and when he put the plugs back in he put the plug into the socket, the socket onto an extension, and the extension onto an impact wrench and drove the thing into the head, didn’t even bother to thread it first…
Seperate incident but my brothers Civic came back from the Honda dealer with spark plugs that wouldn’t come out too…so…
I trust dealer mechanics (any mechanics for that matter) about as much as I trust cops 
Bitter? gee, ya think?