I sent my best technician to do a tile & grout job. He clean with an akaline product (StoneTech's Cleanzall). We scrub ever grout line and use our Boxxer 421 at 1000 psi and great heat. We hardly ever get callbacks on tile & grout. Well she did. My technician went back to the house and the grout looked great. There were a couple of minor spots in kitchen. So he went with and acid and recleaned the entire kitchen. She called back again and said it still doesnt look good enough. What would you do????