On the IRS site they have rules governing how to audit a variety of industries. It even goes down to how many gallons of water a commercial washer uses so that they can check up on laundromats. I'm not in any of the professions listed but I'm sure others are. I think its a hot deal, it's free and will save you money.
http://www.irs.gov/businesses/display/0,,i1=2&genericId=7045,00.html
http://www.irs.gov/businesses/display/0,,i1=2&genericId=7045,00.html