Every 30 minutes we read the cheapest listings on offer in each category and record three numbers: the cheapest price, the median of that cheap cohort, and the highest price inside it. So "median" here describes the cheapest cohort only — it is not the average price across the whole market. The listing count is the full live count for the category.
Prices move hourly and listings sell fast. Treat every figure as "at the reading time" shown, not as a promised price.