I am very wary of this myself as I have had 4 experiences with the local discount tire stores scratching up the faces of wheels on a few of my family's cars. The closest store to me is terrible about this and has scratched our wheels on 3 occasions and each time tried to deny the fact that there machine caused the damage. The other location gouged my aftermarket wheels, but did replace the entire set.
Now I only go to a performance shop in Ft. Worth, 1 hour drive for me, but they use a Hunter mounting machine which does not hold the wheels with metal claws in the way the machines at most shops do. If you are truly concerned about wheel damage find a shop with a Hunter.