[dolel13]

A schengen visa doesn't allow you to work. At the moment, it only grants you a stay of upto 90 days in the schengen area and for most countries, it's not possible to change the visa once you're in the country. If you want to work, you're required to go back to your home country or outside the schengen area and apply for a work visa/permit. All this is based on the assumption that you're a non EU/EEA national

[jotm]

That really doesn't stop those who are desperate for work. They "visited" Hungary or went to "buy a car", and then hightailed it to Italy, Germany, Netherlands to work illegally. Not sure how they got back home, probably deported and banned...

But in this case, to work legally, he'd need a work visa as you say, which I imagine is even harder to get?