Hi Circuit, you have a few options: Zillow, Realtor CMA, or Appraiser. If I were to make "accuracy analogies", I would compare Zillow to the game of Horseshoes; a Realtor-CMA-with-narrative to Darts from three feet back; and an Appraisal with competitive archery.
â€œHorseshoesâ€ a.k.a. Zillow:
Zillow describes their "Zesstimate" as a "starting point." While I applaud their efforts to inform the public, quite frankly, for those that seek relative accuracy Zillow is a data source I would completely avoid.
For example, for San Mateo County here's Zillow's Accuracy:
Within 5% of Sale Price - 26%
Within 10% of Sale Price - 46%
Within 20% of Sale Price - 71%
Median Error - 8.7%
You might want to apply some of the stats above to the purchase price you are looking at to get a relative error value in dollars.
"Darts" a.k.a. Realtor CMA:
I believe the Zillow data above shows estimating a home's value based solely on numbers does not work because it completely discounts the qualitative aspects of a home, and that's a huge mistake because while price is important in buying a home we all know location, amenities, look and feel play a large role in determining market value as well.
If you are serious about accurate valuations you must be working with a licensed Realtor with a little "scar tissue" in the area you are looking in. A Realtor can prepare a Comparative Market Analysis, which other than an actual appraisal, is the "gold standard" for approximating market value - period. A Comparative Market Analysis (CMA) gives you the best representation of market price/activity/trend direction - for the specific search property details you search on (i.e. 3 bed, 2.5 bath, 1500-1800 square feet, etc.). Keep in mind that just because a property sells right next door to another does not mean that it's a comparative match.
Also, DO NOT rely on median-based statistics, these measures are meaningless for targeted selling/purchasing as they have no regard for any of the specifics you may be comparing and can be skewed by segments of market activity not matching your individual situation. A â€œmedianâ€ is defined as â€œthe number separating the higher half of a sample from the lower half.â€
For example, letâ€™s say three homes sell in a neighborhood for $400K, $425, and $575K in one month. The first two may be neglected REOs, and the third has been maintained beautifully. The current monthly median value for this neighborhood becomes $425K.
A buyer/seller should look specifically at the targeted segment of properties that match their search criteria for the information to be meaningful. Generalized stats are easier to come by, but that doesnâ€™t mean they should be used to make one of the most important financial decisions of your life.
Best of all, a Realtor will do this for free!
"Competitive Archery" a.k.a. Appraisal
While I would not advise it due to the $350-$400 fee and the unknown probability of having your offer accepted by the Lender(s), an Appraisal would hold the highest level of accuracy. Addtionally, given the timeline for short sales can be very long (4-12 months) the appraised value might be "stale" once the lenders' approval is granted because the value is based on the date performed! So, you very well might end up wasting your money.
In any case, if you would like to find a professional appraiser on your own you can find one here (or ask your Buyer's Agent): http://www.orea.ca.gov/html/lic_appraisers.asp
There are four levels of real estate appraiser licensing (below).
AT - Trainee License
AL - Residential License
AR - Certified Residential License
AG - Certified General License
You can see what is required for each level here: http://www.orea.ca.gov/pdf/Upgrade2008.pdf