Say you were going to sell your house, but first you have me do an appraisal for you. I would bet with most certanty, that the final sale price you agree on with the buyer would not be the exact appraised value I gave you ahead of time. It may be off a few percent. This is the same thing as me appraising a house for 1-2% higher than what my orignal opinion of value was.

This is no big deal and is in now way even partially responsible for what has happened to the real estate market. Fraud and price inflating, on the other hand, has contributed to the issue.