At the income levels I deal with, people erred in their own favor, usually unknowingly, sometimes because they were told by promoters, etc., and then received that goverment letter. The clients that did a rollover and didn't report it, but maybe had 20% W/H so that'll be taxable. The NY commuter who worked from home and didn't report it as NY-sourced income. The OIH who used the same area % as the depreciation % (that was a HRB preparer doing returns on the side from their kitchen table, paper and pencil, for a baker using her home kitchen on Saturdays, not regular nor exclusive anyway, but 25% ?! Whole house'd been depreciated in four years long ago!). The IRA distribution with 10% W/H who didn't report it "because I already paid taxes on it." The multi-state returns that didn't start with federal AGI but just with their income in that state. The SE that deducted 100% of their car or their cell phone or.... Those ladies who sell clothing or make-up or...at home parties and deduct their own products and the furnishings they bought for their living rooms to show their products and their vacations where they wore their products or.... The losses reported on sales of primary residences. Have one now who got caught in 2010 for 2008 not reporting his investment income; but he didn't amend NY and CT. Now, NY wants as much in taxes, penalties, and interest, as his unreported income was! And, it's too late to get him a credit in CT for 2008. Yeah, when I fix the DIY, it costs them more.