The core data points to track are item identity, price, stock status, listing date, and sold date. Item identity means brand, model, year, and condition. For equipment, you may also need to track phase, cooling type, or other specs that affect price and usability.
Stock status means in stock, out of stock, or sold. Listing date is when the item first appeared. Sold date is when it flipped to out of stock or was marked sold. The difference between listing date and sold date is velocity.
Tracking these fields over time creates a historical record that reveals velocity, pricing trends, and inventory turnover patterns. A single snapshot tells you what a competitor charges today. A historical record tells you whether they raised or lowered the price, how long the item sat, and whether similar items are moving faster or slower.
The organizational challenge is deduplication, normalization, and change tracking. Deduplication means recognizing that the same item may appear on multiple competitor sites or in multiple listings. Normalization means handling the fact that different competitors may describe the same item differently. One may list a machine as a 2010 model, another as a 2009 model with a 2010 serial number.
Change tracking means capturing when a price changes, when stock status changes, or when a new listing appears. Without change tracking, you cannot see velocity or pricing trends. You only see the current state.
For small catalogs, a spreadsheet with manual updates can work. For larger catalogs or more frequent checks, manual tracking becomes impractical. The time cost and the risk of data-entry errors both increase.