Here in Denmark, there was a case that a carpenter or another skilled tradesman decided to build something on his house. Like any other tradesman he would do it himself, because why the fuck not?

Well, someone somehow complained about it, courts got involved too, then the tax men came creeping out of the woodwork saying that because he was "trained" in it. it was under the table work and needed to be paid income tax on it... For working on his own damn house...

Using your own labor for your own good is not allowed, the tax leeches wants their blood.