What can I tell my customer when they ask if they can use glass cleaner to clean their marble shower walls?

Tell them simply this: “No, I would not recommend using window cleaner on a marble shower wall. Some window cleaners contain chemicals which could damage the marble.” Also, let them know to keep their marble shower walls in optimal condition the very best thing they can do is this: spritz on a little Stonecare PRO Signature Daily Bath and Shower Cleaner or Neutral Cleaner, then squeegee the walls down after everyone has showered for the day. If mildew ever becomes a problem, recommend Stonecare PRO Signature Mold & Mildew Stain Remover, and if heavy soap film or mineral deposits ever become a problem, Stonecare PRO Signature Heavy Duty Soap Film Remover is a great product.

TIP Some window cleaners contain vinegar. Vinegar contains acetic acid which can etch a marble surface.