eBay market price discovery
The most reliable comp for an eBay card: sold listings (filter "sold" in advanced search) from the last 30 days, same card, same grade, same edition. Average those prices. That's your expected value.
If a current listing is 10%+ below that average, it's a bargain. If it's 20%+ below, it's either wrong, stolen, or the seller doesn't know the market (investigate before buying).
Auction vs buy-it-now strategy
Auctions: Win 40% of the time, pay 5-15% less than BIN. But you tie up capital until the auction closes (7 days standard). Best for high-value cards ($500+) where small percentage savings add up.
Buy-it-Now: Instant payment, instant gratification. Prices are usually 10% higher than auction average. Best for cards under $300 or when you know the comp and want to lock it in.
Timing and seasonality
Card prices drop 15-20% in January-February (post-holiday cash burn, New Year's resolutions cause liquidations). They peak May-July (summer break, new releases, playoff season). August-September (back to school) sees a secondary dip.
If you're buying to hold, January is the time to load up. If you're buying to flip quickly, May-July gives you a bigger window to exit at higher prices.
Comps & PriceCharting
PriceCharting aggregates recent eBay sold listings and shows the trend. It's free and the most reliable comps source for sealed products. Use it to find cards trading 20%+ below the 30-day average — that's where the flips happen.