Why are we forced to accept increases in our property taxes when real estate values are...?

In our locale, a few year back, a similar thing happened. AND, we heard that the municipality was giving people a hard time who were appealing the valuation of their homes. So, we hired an appraiser for $200 and had a very rudimentary appraisal done. The appraisal came in well below the city's valuation especially after recent sale comparables were factored in. We then found out that the city was obligated to lower the valuation in light of a professional appraisal. There was no legal room for them to give us a hard time, so they didn't--they lowered it immediatley! It reduced the taxes so much that we more than paid for the appraisal. I don't know if this works any other places, but it sure worked for us. At any rate, always appeal the valuation since you have nothing to lose. I know one guy who appealed his automatically regardless of what they said it was worth, and many times they just lowered it rather than go through the time and expense of disputing it. A bit gutsier than I care for, but it worked for him.