Haha, I recall seeing a similar plot with a "suspicious discontinuity" when I looked up data on home appraisal price vs sale price. I remember asking the loan officer why the contract was forwarded to the appraiser before they did the appraisal, because that might bias their assessment. She gave me a funny look and replied "that's kind of the point."
Then again, the finished house then appraised at $50k _over_ cost 12 months later when I converted the construction loan, so maybe the first appraiser really was nuts.