At the dealerships these days, they use torque sticks. It's an attachment
that goes onto an impact gun. The gun will jump when the proper torque has
been achieved. And,... it will go no farther.
If you don't torque the lugs evenly, your rotor can warp.
Just because you saw them use an impact gun, when they tightened the lugs,
it doesn't mean that they did it wrong. If you see a 6" to 8" extension on
the gun, they are doing it correctly.
P.S. Unless you purchase a torque stick for your impact at home. You should
use a torque wrench to tighten your lug nuts.