Zillow's Zestimates are particularly obnoxious because they provide little detail regarding why the values change and they retroactively revise them. I bought

Zillow's Zestimates are particularly obnoxious because they provide little detail regarding why the values change and they retroactively revise them. I bought a house this summer that had an inexplicable drop in estimated value of about 15% a month or two before the house was listed. I paid closer to the previous estimated value than the post-drop value. Now when I look at the house on Zillow, the drop is nowhere to be seen and the past year is a smooth, barely sloping line. Never was there any indication of why they had a 15% drop, which was particularly frustrating when trying to determine how much to offer for the house.