In Europe nowadays it is better to have a white vest - means pay your tax and social security. Europe has become(it always was ^^) very small and normally it is hard to hide if they are once tracking you.
15-20 years ago it was easy, even 10 years ago still possible without really having sleepless nights. I would not risk getting called in front of a court for social security violations(tax wise it is even worse).
Don't get me wrong - I know that people are still doging the system, but I don't think it is a wise thing to do. I do know pilots that earn 10k++ in Russia flying for an owner, still having a fake job back in central europe(don't want to specify, but it is a very social state) so they safe peanuts on social insurance.
And building houses. One day the tax office will knock on their door and asking how it is possible to build that house and nice car on 500 Euros/month. But some never get enough and eventually they will pay(a lot).