Schematic: D.U.C.K.O.Y.

Fair value is the item's region-wide daily median, weighted over the last 14 days (recent days count more, half-life two days). When history is too thin we fall back to the current market median instead.

The verdict compares today's cheapest buy with fair value: 30% or more below is a deal, 10% or more below is cheap, within ±10% is fair, anything else is above.

A deal reaches the Deals board only when the estimate is at least medium confidence and there are at least 5 listings.