Validation
Every trust claim in one place, and how to check each one.
Every claim on this site is checkable: the error rate is measured on held-out sales, the engine is deterministic, and any certificate can be recomputed by the person you send it to.
Back-tested against real sales
The active methodology (rev 4.13) is scored on 218 recorded sales held out of the engine's evidence for back-testing - sales the model never saw. With each sale withheld from the engine's evidence, median absolute error is 85.1% and 29.4% of estimates land within a factor of two. That is the published figure and the one to plan against. If the engine already held the sale - the same sales with each one's own sale added to the engine's evidence - it reads 26% and 94%. The full table, including where the model is weakest, is public.
Deterministic by construction
Same domain, same answer, every time: the engine scores 200+ structured signals with no randomness and no wall-clock inputs, and CI gates enforce that property on every change. Any number on this site can be reproduced by running the same appraisal again.
Certificates anyone can check
A locked-in price becomes a numbered certificate that cannot be quietly edited. Anyone you send it to can recompute the number themselves - no account, no trust in us required.
A worked example, end to end
A real sealed certificate from the reference edition, shown read-only: the price, the factor scores, and the public check anyone can run against it.
Reproduce an API response yourself
The Open Domain Valuation Standard pins every appraisal to three SHA-256 hashes. Paste a real API response and recompute them in your own browser - no account, no server round-trip, so a match cannot be manufactured by the site that produced it.