Our company works with a Ceramic coating that is very versatile. It is an Energy Star 'Cool Roof' coating but does way more than just roofs.
20 years ago I made the demonstration sample you can see above. I pulled it out of a scrap pile at a remodel job site. This is by far the best sales tool I have ever had.
I took it home, cleaned it off and painted one half with our coating. I cut a piece of 3/4 inch plywood to fit tightly inside to divide it into the two sections. Then I stuffed R-19 fiberglass in it and filled up both sides.
I always kept it in the back of my truck. If I had an appointment with a prospective commercial customer with AC units and ducts on their roof, OR a metal building or other metal structure, I would make my pitch with my book and then take them outside to 'Feel the difference' in the temperatures.
I always had them feel the coated side first. With very few exceptions they would always touch the coated side with their fingertips quickly, then p[lace their entiire hand on it, nice and cool to the touch. Then I would ask them to touch the bare side. Again, in almost every case, they would place their hand flat on the bare galvanized metal, for about 1/2 second. On a 100 degree day it would be in the 180 degree range. They would yank their hand back quickly, many times cussing at me for not warning them.
If that demonstration did not sell the job right then, it always gave an effective enough demonstration that they would allow me to do a test patch on their ducts or roof. Once they felt the same kind of temperature difference on their building or their AC unit / ducts, they were sold.
'Their building'. I cant count how many times I have opened my pitch book, showed them pictures, statements, energy calcs, etc, just to have them say "OK, but what's it gonna do on MY building?"
You can show them overwhelming proof on paper and you can talk and try to educate them until you are blue in the face and they still might not be sold. Give them something to feel, they know the difference between cool to the touch and painfully hot. If they burn their hand, they will also never forget you OR that demonstration :).
The least amount I have EVER dropped the air temperature coming into a building, by coating a rooftop AC unit, is 5-degrees, the most was 25-degrees.