In Israel I needed to get an appraisal for my collection for insurance 
purposes.  I asked my insurer who could supply the appraisal and they 
gave me a list of appraisers.

I contacted one of them, paid him his fee, and referred him to my piano
technician for information about the value of my instruments.  Would 
you believe it, the appraisal came out to exactly the amount that my 
piano tech said it was.

I just purchased an apartment and had to have it appraised.  I called a
real estate appraiser, who came and looked at the apartment, then gave 
an appraisal for $30k less than I paid.  I really needed the full 
amount for the loan, so I took another appraiser.  He actually measured 
the rooms and appraised the apartment for $20k more than what I paid, a 
difference of 10%.  

They will tell you that they have exact methods; but in my opinion it's 
simply throwing the dart at the dartboard and giving an answer.

Eli