It's stupid comebacks like this that make you a target..... and an example.
Murphy's Law comes into play on this one. There's never time to do it right, but there's always time to do it over.
You say you have some automotive painting background. Well, good for you, because you really need some common sense background. You realize by repainting it, you need to go there once to get all your site survey information. Then, you put all your numbers together. If they accept, you need to go back and take the 2 signs down. Now ya hafta clean them, prep them and paint them. Now, ya hafta print and apply your prints. Next you need to go put them back up.
There's no way in heck you can do all that for less than using brand new panels and having 100% substrates to work with, not to mention how long ya hafta wait for your paint to cure entirely so there's no lifting. One less trip and about a 1/4 of the supplies needed to do the job.
He was wrong, you aren't taking customers off our hands, you are creating dumber customers by giving them false hope with your nonsesne.
Besides, you already have the attitude, just a stupid one.