Appraisals are completely inaccurrate. They take comps from around the area and once over of your place and put a value on it.

I've seen appraisals of the same property vary by as much as +/-25% based on which comps they choose and the appraiser's mood that day.

Going into our last housing bubble, appraisers were not estimating true value of a propery but propelling it ever higher because of short supply. Every new sale lifted the prices higher because every appraisal was based on a previously inflated sale price in the area.