Resale price sites give you one number with no date, source or sample size. SoldSignal is a free weekly index for 30 sneakers, consoles, collectibles and watches from GOAT, StockX, Mercari and Chrono24. Every price shows SOLD vs ASK, how many data points it comes from, and what a seller keeps after each platform's fees. Free JSON/CSV API with no key, a fee calculator, and weekly archives.