I would have the trigger thoroughly cleaned using an ultrasonic degreaser/cleaner before I would have any work done on it.
I knew a guy in Smackover AR who did trigger jobs on S&W. His technique was to remove the side plate fill it with break free and a fine grinding compound. Have the owner shoot a 100 rounds or so and bring it back. He cleaned the stuff out, ensuring all the grinding compound was removed, and gave it back to the owner.
The S&W M-15 I shot which he had treated had one of the smoothest actions I ever felt.