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Shopping & ErrandsAny

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.

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Use case overview

An engineer built a Codex agent that browses eBay listings, extracts PSA certificate numbers and cross-references known prices while he sleeps.

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Reported experience

  1. 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.

  2. How it went

    It works as his power buyer, surfacing underpriced cards before others see them.

  3. Worth knowing

    Limit batches to 5 listings to avoid eBay bans; run on a cloud VPS.

Example prompts

Try 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.

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