If the value of your CU property has dropped, the SC County assessor office will send you an ammendment.
For Cupertino if the price drops 1-3% for the same size, and you are forcing the issue by contacting the office
you may get an adjustment. From what I recall once you challenged the authority your property will quickly get adjusted and watched for a re-assessment in an up swing. That happens to one of my clients.

As for collecting comp data it is better to get a State Licensed Appraisal who does it correctly and is qualified to represented you.

I don't think home prices in the zip code 95014 has dropped!!
There is deadline for submitting application for adjustment of property tax, make sure you haven't missed that!
Mehdi Safipour
408-857-2709

Mtn Rain -

If you go to the tax assessor's web site (http://www.sccassessor.org) you will find a form to complete. You will need to support it with like homes that have sold within one mile of your home in the last 12 months. They are looking for a change in value tax-year to tax-year. Have an agent that works in your neighborhood assist in pulling comps. I have done this before for folks.

http://eforms.sccgov.org/lfserver/DeclineInValueRequest

Make sure to click the "more information" link near the bottom of the page it outlines how your application will be reviewed:

Good luck!
CJ