You can file a request for an assessment reduction yourself, but an attorney with good negotiating skills should be able to reduce the assessment even further. California state law allows a fee perhaps as high as 50%, but generally the agreed-upon payment ranges in the 33% range.
I see you are in San Jose, assuming your property is also in Santa Clara County, take a look at the link I have included on Proposition 8 Temporary Assessment Reduction which includes quite a bit of info on what to do.
Generally, you need to apply and appeal before September 15 of the calendar year you are disputing. You must show the property value has declined as of January 1st of the calendar year, so, for example, for 2008 taxes, you must show that the value of your property on January 1, 2008 value was lower than the assessed value.
There may be other facts involved that would change the September 15th deadline for your situation.
DISCLAIMER: THIS IS NOT LEGAL ADVICE NOR DOES IT CREATE AN ATTORNEY-CLIENT RELATIONSHIP.
I AM LICENSED TO PRACTICE LAW IN OHIO AND UTAH ONLY. THIS IS ONLY GENERAL INFORMATION AND IS FOR EDUCATIONAL PURPOSES ONLY.
Each State/County or other taxing authority has its own rules on appealing a tax valuation. Generally, the taxing authority has a website where you can find those rules. Depending on the taxing authority, you may want to call that office and ask about the process. If you do so, remain calm and as pleasant as possible. Explain that you just got the assessment and do not understand how it was developed, ask for help. Avoid accusatory statements, etc. as this will not help your efforts to get the facts, and you will need the facts. If there is a clear error you may even be able to get resolution easily and quickly without any more effort. If it is a matter of policy (all values are increased by a given percentage) or judgment then getting a change on a single property will be difficult.
There is most likely a time limit established within which a party must appeal the valuation. Sometimes the appeal can be made by written documentation while at other times it requires a “hearing” before a board of review. A timely request for review or hearing is essential to protecting your right to further appeals.
When calling the taxing authority try to get the person to whom you are talking to go over how it did its valuation and to get as much information that you can about the process. Avoid any personal attacks — keep it calm. You will need all of this information to make a credible challenge. You will need to show that there is a clear error as the taxing authority gets the benefit of presumption that its decision is correct. You have the burden of both providing evidence of the error and that the evidence is sufficient for the taxing review authority to make a change.
If the matter is of significant value you would likely want an attorney to represent you. Legal fees can vary from under a $100 per hour to well over $500 per hour depending on the expertise of the lawyer and location. A hearing may only take a few minutes but the preparation time may be significant. That is why it is important for you to do as much fact gathering as possible, this will reduce the time that attorney or staff will devote to the matter.
An attorney that charges a fee based on success (contingent fee) may be a good alternative depending on the amount at stake. If the tax increase was a few thousand dollars, then the contingent fee type of arrangement, even at 40%, may be reasonable compared to an hourly rate kind of fee. Often, the contingent fee lawyer may devote all of his/her time to these kinds of matters and may get a more favorable result based on past success and relationships with the hearing board. If the attorney is despised by the hearing board then you could get an opposite effect.
You can always represent yourself which is generally not a good idea due to the emotion that could come into play and lack of experience with the process.