Been scanning item marketplaces for a while now and there's one mistake I see constantly: people compare active listing prices across marketplaces instead of completed sale prices.

Here's why that matters. An active listing tells you what someone wants — it tells you nothing about what buyers are actually paying. I've seen items sit listed 15-20% above their real trading price for weeks because sellers anchor to an old high and nobody corrects them. If you buy based on listings alone, you'll misjudge your margin constantly.

The fix is simple: before you count any trade as profitable, pull the last 5-10 completed sales on your sell-side marketplace, not just the current listings. That's your real fair value. Compare that number against your buy price, subtract fees, and now you have an actual margin — not a guess.

Second thing worth flagging: liquidity windows around content updates and esports events are where the fattest margins show up, but they close fast. If you're not already watching for those specifically (not just generically scanning all day), you're leaving the best trades on the table.

I put together a full breakdown of this — the fair-value calculation, margin thresholds, and a repeatable scanning workflow — inside Loot Ledger Arbitrage. If you want to go deeper than a forum post can cover, there's a 1-day free trial to check it out. Happy to answer questions here either way.