You don’t have to believe the IRS
The IRS mails millions of letters out to taxpayers every year. We kindly refer to these as nastygrams. There are around 76 different types of letters you could get. http://www.irs.gov/Individuals/Understanding-Your-IRS-Notice-or-Letter.
Each has a notice number that only the IRS seems to know about. They tend to treat you like an idiot if you don’t know what notice number you got. (It’s in the top right corner of the first page of any IRS letter.) Most of the IRS letters tell you that you did something wrong or you owe them more money.
Our experience is that the IRS is often wrong. That means that statistically, even they can get it right sometimes. That being said, never trust what the IRS letter is telling you without consulting with a tax professional.
Too many people send them money when they don’t actually owe them money. And guess what, the IRS isn’t really going to be very quick about telling you that you overpaid them.