@David Krulac - A common misconception about appraisals is that they are supposed to be absolutely accurate. Another misconception is that they are ordered because the parties invloved have no clue what the value is.
As for accuracy, the industry considers an appraisal accurate if it is within +/- 10%. Thats a 20% spread in the range of value if the property is valued in the middle. I have seen markets where the range of value for similar properties can be much, much more. Another aspect is that an appraisal estimates the value of a subject property by incorporating the sale prices of other properties. Ever see two properties exactly similar? How about the human dynamic? One realtor might price high to get a larger commision while the next might price low to get a faster sale - you wont see that line item adjusted for in an appraisal. I could go on and on.
All of this brings me to the second misconception. You may ask, if an appraisal is most often not absolutely accurate, what's the point in the first place? The answer is two part. First, an appraisal is only reasonably accurate, and what is reasonable is decided by the client who orders the appraisal. The accuracy needed determines the scope of work (or level of research and analysis). In the case of a mortgage appraisal, the lender knows full well the reliability of the appraisal (which is one reason they only lend 80%), but for them it provides accuracy within a certain parameter. How many borrowers would you suspect would be willing to pay $1000 or more for an appraisal? There is a balance to the system that often gets overlooked. The second part of the answer is why 99.999% of all residential appraisals are ordered in the first place, dishonesty. The appraiser is the person who does not have any interest in the outcome of the transaction. Their fee is not tied to the value as most all other parties are.
So, calculating a value is not the main reason appraisals are ordered. The majority of people on this forum can estimate the value of a property as competently and accurately as any appraiser. An appraisal is nothing more than a tool for lenders and municipalities. If people were honest, there would be no appraisal industry.