"deliberately damage my sump plug in order to sell me an expensive repair"
Most likely the damage was done by over-enthusiastic tightening (as opposed to applying the correct torque) the sump plug at the last oil change, repairing the sump is never a manufacturer authorised repair so the tech would be recommending the correct repair if it was a franchised dealer. Obviously your vehicle means it's your choice, I have known repairs like that to be done as 'goodwill' if the vehicle has always been serviced within the dealer network - if the owner pushes enough....
Biting the hand that feeds IT
