Shaking is due to a misfire of one cylinder. Sensor data causes the engine computer to adjust fuel metering to all cylinders equally.
The dealership mechanics are highly trained to find the problem quickly without blindly throwing a bunch of parts at it. Sensor information is read with a hand-held $6200.00 computer to speed the diagnosis. That's part of the expert service you're paying for which very often in the long run is the least expensive and fastest way to properly diagnose and fix the car.
How many miles on the engine? How long since the spark plugs and wires were replaced?