Zestimate is the biggest mess and they can't fix it. It can be way off, by over 100 grand, and they have one excuse after another. I have a professional appraisal to prove it. Zillow is very unreliable and their data can't be trusted. Customer service ignores customers. They don't help For Sale by Owners and can cost the owner several thousands of dollars by misleading buyers. Their system gives priority by sending contact information about real estate agents instead of the owner. I have had buyers tell me they were mislead. Beware of this system it can cost buyers and sellers thousands of dollars. I wish there was an option to give them less than a 1 rating.