Does the appraisal information from the tax district reflect a home's value?

How many times have I heard a buyer refer to the Harris County Appraisal District's appraised value of a home -- especially when the appraised value is quite different from the sales price!?  I hear this most often when the value is far below the asking price of a home.  I have to educate the buyer that while this is value is called "appraised value" -- it is actually an "assessed value" from the taxing autorities.  Homeowners want to keep the assessed value as low as possible, and it is our right to protest the property taxes every year to keep them from sky-rocketing.  However, an appraised value fluxuates as the market fluxuates.  The home value should be based on the condition of the home with respect to other sold properties that are the most similar (i.e. true "comps" -- or comparable sales) in the area during the past 3-6 months.  These are the values an appraiser will use to arrive at an appraised value when assessing a home for a mortgage or refinance.  It is not the same process used by the county's tax assessors.  To be honest, I am not sure what process the tax assessors use, but I am quite certain it is not at all in depth.  Even the square footage quoted on the tax records is often inaccurate, where an appraiser comes in and measures the home in detail, and provides a written record to show the calcuations. 

The bottom line I want to communicate here is that when you are purchasing a home, definitely look to see what the tax assessed value is, but use this as information only.  It should not alone establish the market value.