Window tinting def. takes a sometime to learn to be able to do things right. Cutting isn't terrible... but the shrinking of back windows is a talent as well as being able to fix an early bubble etc.... outsource it....
One of my best friends owns his own tint company, and we happen to be renting a shop together, so he quotes me a semi discounted price, say 160 and I charge 200-225 (example). While trying to upsale the detail etc and vice versa for details upselling tint. You may only make 40-65 bucks more, but you didn't do anything but make an app. and a receipt. 3 cars a week=$120 times 4 weeks, 480-500 more in your pocket.