First, have the customer sign a scratched glass waiver. Then, put some undiluted ammonia in a spray bottle (I wear a respirator and make sure the room is well ventilated), spray the tint liberally then apply a piece of black plastic (I use trash bags) on top of the wet ammonia. Let it sit a while (at least 30 minutes) when you go back to the first window, get a corner started with your scraper, and SLOWLY pull the tint and trash bag off the glass. If it starts to get harder to pull, spray more ammonia. Sometimes you might even have to do a combination of additional spraying mixed with pulling and scraping. After you got the tint off, I apply my regular solution and scrape and bronze wool the glass before squeegeeing. This is the best method I have used, and I have tried oil flo, heat guns, water and scraper and even dry scraping. This process works best for me. I hope you are charging accordingly!