Upvote:1
Europe's a big place, so I'm generalizing with a wide brush here, but if you work illegally, you're likely to get exploited, the chances of getting busted are high, and the consequences are severe.
First, if you're working illegally, you have no rights. You can get paid less than minimum wage, not be paid what you were promised, be made to work illegal hours or in unsafe conditions etc, and because you're working illegally, there's nothing you can do (except quit). So this alone is a gamble and quite potentially dangerous.
Second, surprise labor inspections of industries that often employ illegal workers (restaurants, construction etc) are common, and the visas of workers are regularly checked. If you're caught working on a tourist visa, you can expect to be deported and blacklisted from returning to the EU.