reputation
We just know this personality type too well to risk our reputation on them going around town or online bad mouthing us because the top quality vinyl kit they bought failed and it just had to be the installer's fault.
I had a guy with a $100k Porsche want us to install a kit for him and I simply told him that we'd do it but unless we produce the graphics, we would make him sign a waiver releasing us from any harm or graphics failure. He moseyed down the road and I'm sure one of our competitors did it without blinking.