. . . look at Italy.
Quiet, simple, no heavy penalties, nothing required from the taxpayer which would rat out someone else.
Ninety! Five! Billion! Euros! declared, and another € 30 billion expected because they extended the deadline from 15 December 2009 to April 30, 2010.
Your long-term profit-maximizing strategy is to get people legal, declared, and on the table. Then you’ll collect income tax during their lives, and estate tax when they die.
Your profit-maximizing strategy is not well-served by enticing volunteers to step forward then
poking them with a pointed stickdropping a 16 ton weight (YouTube) on their heads.