Flat tax is the best way to tax people that show incomes. The problem is when you go to flat tax, the reported incomes will go down. I will use myself for an example. 65% of my income is cash, the rest is traceable income. For those like me, that generat cash income, the reported income will go down.
The ultimate way to make a fair tax is the national sales tax. That will foster investment and savings among the citizens. If you don't spend then, you don't pay tax. I love it!!