Shopping & ErrandsDone with Codex Jul 18, 2026
Hunt high-value Pokémon cards on eBay overnight
An engineer built a Codex agent that browses eBay listings, extracts PSA certificate numbers and cross-references known prices while he sleeps.
- What They Did
- Alessio Finelli gave the Codex agent a sparse skill file with rules on target cards, batch size of 5, and grading companies. The agent browses eBay listings on its own, extracts PSA certificate numbers, cross-references known prices, and flags underpriced high-value cards. He steps in only to review flags for his physical shop.
- How It Went
- It works as his power buyer, surfacing underpriced cards before others see them.
- Worth Knowing
- Limit batches to 5 listings to avoid eBay bans; run on a cloud VPS.
Try it yourself with Codex
Write and run an agent that browses [marketplace, e.g. eBay] listings for [item type, e.g. graded Pokémon cards] under [max price], extracts each listing's [certificate or serial number], and compares it to prices in [price source or file]. Save listings that look underpriced by at least [percent]% to a file called [output file] with the link, price, and reference price. Stop after running it once on [number] listings and show me the results and how to schedule it overnight. Don't buy, bid, or message any sellers.