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Appraisal vs Zestimate and other AVMs

An automated valuation model is a statistical estimate produced from public records, tax data and prior sales. It is genuinely useful, it is free, and it has never seen your house.

What an AVM is good at

Uniform housing, plenty of recent sales, accurate public records. A 1990s tract subdivision where four hundred houses were built to six floor plans and thirty of them sold last year is a market a model can read well. Honestly, better than a rushed appraiser.

AVMs are also good at scale and at speed, which is why lenders use them for low-risk decisions, portfolio monitoring and pre-screening.

Where they fail

Anything unusual. The further a property sits from the statistical middle, the worse a model performs. Waterfront, acreage, custom construction, historic property, unusual lots — these are exactly the properties where the model has the least to learn from.

Renovations and condition. A model cannot see that a house was gutted and rebuilt in 2023, or that another has original 1978 finishes and a roof at the end of its life. Two houses with identical records can be a long way apart in reality.

Bad public records. Models inherit the county's data. Where square footage is wrong, a permitted addition was never recorded, or a garage conversion is not reflected, the model is confidently wrong.

Thin markets. A small community with two sales a year gives a model nothing to work with, so it borrows from a wider area, and the wider area is a different market.

South Florida makes all four worse

This is not a general complaint about algorithms — it is specific to where we work.

Waterfront is not a checkbox. Whether a slip exists, what it can hold, the water depth at low tide, and whether a boat can reach the inlet without meeting a fixed bridge produce very large differences between properties a model sees as equivalent.

Postal city is not municipality. Large parts of Palm Beach County have mailing addresses that do not match where the property actually sits. The Acreage alone has mail addressed to Loxahatchee, Royal Palm Beach and West Palm Beach — one community, three cities. A model grouping by mailing address will compare an acre-plus Acreage parcel to tract housing inside Royal Palm Beach's town limits.

Condominiums carry association risk. Since Florida's 2022 reforms, milestone inspections and structural integrity reserve studies drive assessments that move contract prices materially. That lives in association documents, and no AVM reads them.

Acreage improvements are invisible. In The Acreage and Jupiter Farms, barns, paddocks, workshops and outbuildings can carry real value and appear in public records as nothing more descriptive than "outbuilding".

The honest comparison

An AVM gives you a fast, free, unaccountable number with a published error rate.

An appraisal gives you a slower, paid number produced by someone who stood in the property, chose the comparables deliberately, wrote down the reasoning, and signed a certification they can be held to.

For "roughly what is my house worth", the AVM is fine and I use them too. For anything where somebody will contest the number, it is not evidence.

A practical suggestion

If your AVM number looks wrong, check the public record first. Go to your county property appraiser's site and look at what they have for square footage, bedroom and bathroom count, year built and lot size. Errors there are common, they propagate into every model, and correcting them is free.

What is a home appraisal? · Market value vs assessed value · How appraisers choose comparables

Matt Thoren, State-Certified Residential Appraiser. 561-853-2129 · Residential only.