IRS doesn't audit 12 years of returns unless something's questionable

Bloomberg - Donald Trump’s disclosure that his tax returns have been under review by the Internal Revenue Service for the past 12 years reflects a “very unusual” level of scrutiny by tax authorities, according to a former Internal Revenue Service agent who now works as an accountant for wealthy people.

“He signed his name to a return in which the IRS is finding problems for the past 12 years,” said Alan Olsen, the managing partner of Greenstein Rogoff Olsen & Co. LLP, an accounting firm in Fremont and Palo Alto, California that caters to wealthy Silicon Valley clients.