They don't - they list at an asking price that got picked after a long discussion between them and their realtor, which accounts for what the timeline of the seller is, recent comparable sales, market trends, interest rate forecast, and a ton of other details which Zillow knows little about.

Zillow is fine for a quick ballpark number. Anything else, they are too much of a one size fits all answer to a very unique question - what is THIS house worth?