The only people who dream about asking a builder for a VAT bill in Spain are people who have never been, or have tried it and scarpered back home as soon as they found the country wasn’t for them.
Not rue Rocker some of did try and set an example. I had a successful period in Spain and refused to take part in any black money, corruption or cash payments. It’s perfectly easy to do if you have the will. Just say no and make it clear where you stand. I agree it’s part of Spanish culture, I saw it happening on a daily basis but I found also everyone understood and accepted my personal position.
I am dismayed when I read about the leading political figures behaving in this way but a country in the end gets the leaders it deserves.