Market signals

Listing data tempts you into confusing an observation with a fact. A price on a page is what one seller asked at one moment in one region, not the market price, and a listing that vanished may have sold, expired, or simply been re-posted under a new identifier. The guides in this cluster are built around that distinction: collect the observation, record when and where you saw it, and derive market claims separately where the reasoning can be inspected. Normalization gets the same treatment, because make, model, trim, condition, and currency are all represented differently across sources, and a comparison built on unnormalized fields will look precise while being wrong. Cross-market work adds timing, since regional listings do not refresh on the same clock.