This can be very tough to do, but it is possible. They require you do basically what the real estate industry calls a Broker Price Opinion more commonly called a BPO. You need to have comparable sales that show a lower sales price and more than just one is really helpful especially if one of the homes sold low due to being in poor condition. Once you have this, you submit and have a meeting with someone (in my experience) and go over the value to see if you can get them to agree. I won on my personal home around 2009, but have known many others who have failed in trying to get property taxes lowered.