Holy crap. I never knew Zillow BOUGHT houses! I've always just used it to look at MLS listings. Check Zillow to see what the HOMEOWNER thinks their house is worth. Then check Refin to see what the MARKET thinks the house is worth. As KB said, it looks like Zillow forgot they pad the prices of everything, and starting thinking their price was reality...
Redfin is pretty nuts, too. But again, their guarantee is a lot more cagey - "within 3%, 2/3rds of the time" is basically "we're really right when we're right, and really not when we're not" which hey - that's honest. The proper way to use Redfin's estimates is to see how fucking wrong they are on sold properties. When their "current estimate" is more than a few percentage points one way or another than what something sold for right fucking now you have an idea of which way the market is moving. If you look at how long ago the property went pending, you have an idea when the contract was accepted. Beyond that, it's just noise.