This also creates a really, really strong incentive to look for a job that pays you under the table. Each unreported euro earned is effectively worth two euros

This also creates a really, really strong incentive to look for a job that pays you under the table. Each unreported euro earned is effectively worth two euros (the euro earned plus the euro lost to clawbacks) in addition to any unpaid taxes. Not the kind of incentives a rational policy maker should strive for exactly.