Zillow surfers and real estate listing lurkers alike know one of the online marketplace’s standout features is the Zestimate.

When somebody lists their house for sale, the Zestimate will adjust to include all the new seller-provided info: new photos, details on recent renovations, and, most importantly, the list price.

while a broker wants to list it at a price that guarantees a sale. "If the seller picks a random number that is too high and the Zestimate justifies that, that is problematic," Miller said.

Buying a home looks very different than it did 20 years ago. Instead of calling up a local real estate agent, typically ...