Validation
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 4.9) is scored on 174 price-verified domain sales held out from a corpus of 933 records - sales the model never saw. On the strict generalization cut (the subject's own recorded sale withheld) median absolute error is 85.5% and 28.7% of estimates land within a factor of two; on the like-for-like cut those become 42.9% and 63.2%. The conservative figure is the one to plan against. 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.