zanardi,
The quality of a gun reblue is absolutely dependent on the quality and skill that went into the metal polishing and prepping. Bluing salts merely darken the steel from the natural "silvery/white" colour to a darker blue/black.
Most gun shop bluing services offer two grades: the "hunter" grade, and a "deluxe" grade. The hunter grade is less easily marred, while the deluxe grade is a high mirror polish.
The less expensive polishing work is all done on powered polishing and buffing wheels. The polishing is sufficient to remove the old blue, light rust and discolouration, scratches, and original machining marks. A skillful polishing operator is needed to avoid rounding off edges, dishing out screw hole edges, and marring stamped lettering and markings. The polishing normally stops short of "mirror finish" polishing.
The more expensive polishing work relies heavily on hand polishing using stones and bonded abrasive blocks to preserve marking, edges, screw holes, and parts symmetry. High grade restoration of guns is always done with skillful detailed hand polishing, often followed with traditional slow rust bluing. Final polishing is done on powered equipment using the finest grades of polishing compound to develope the mirror polish.
HTH
John