Sell your home with a Realtor -- make up to 16% more! (Maybe, possibly, sorta!)

A three-minute online infomercial from the National Association for Realtors advises viewers that selling your home yourself is pennywise and pound-foolish. "Realtors," the ad advises, "have the experience to price your home, so it can sell for up to 16% more than selling it yourself."

"Up to 16% more?" The wording is so vague, it could mean anything. It could mean 2% more; it could also mean 5% less. No matter what the actual figure is -- and it's hard to know, because the data is all based on surveys, not controlled studies -- all bases are covered. Having Barbara Corcoran sell your home would probably net you a higher price -- maybe even more than 16%! -- than selling it yourself by Scotch-taping a For Sale sign to your window. But where does that number come from?