Marketplace Arbitrage Score 📈

Score the resale margin on any marketplace listing. Give it a product (or a marketplace search URL) and it pulls the listings, matches each one to eBay price comps, and tells you the spread: what you'd clear reselling on eBay after fees, versus the buy price. Buy-low / sell-high sourcing, in one run.

It generalises the deal-score idea (asking price vs a market benchmark) from property to resellable goods — the benchmark here is the median eBay comp for the same item, matched title-by-title.

What you get

For every marketplace listing (a recordType: "listing" row):

field	meaning
listingPrice / currency	the buy price on the marketplace
compValue	benchmark eBay comp price, in the listing's currency
compBasis	sold (real sold prices — needs your eBay cookie) or asking (live listing prices — the default)
netResale	compValue × (1 − fees%) — what you clear after selling fees
spread	netResale − listingPrice
arbitrageScore	resale ROI % = spread / buyPrice × 100 (positive = profit)
arbitrageLabel	Strong flip / Good flip / Thin margin / Around break-even / Underwater
confidence	high / medium / low (from comp count, price spread, match quality, FX)
matchQuality	how well the listing matched its comps (strong / weak / none)

Plus one recordType: "summary" row per search, carrying the comp basis and the aggregate score (how many listings, how many profitable, best/median spread).

Sold vs asking comps (important)

Since July 2026, eBay shows sold prices only to signed-in visitors. So:

• Without a cookie (default): comps are eBay live asking prices, always labeled compBasis: "asking". Asking prices run higher than realized sales, so the score is optimistic — confidence is capped at medium to say so.
• With your eBay cookie: comps are real sold prices (compBasis: "sold") — the number resellers actually want. Paste your signed-in eBay session into eBay sign-in cookies: either the JSON export of a cookie extension like Cookie-Editor, or the raw Cookie: header from your browser's DevTools. It is stored encrypted and never logged.

The actor never labels a price as sold unless you provided a cookie.

Input

field	required	notes
source	–	craigslist (US, USD) or subito (Italy, EUR). Default craigslist.
query	one of query/URLs	product searches, e.g. ["nintendo switch", "airpods pro"]
listingUrls	one of query/URLs	marketplace search-page URLs, pasted from your browser
location	–	Craigslist city subdomain (e.g. sfbay, newyork) or Subito region slug
ebayCookie	–	your signed-in eBay session — unlocks sold comps
feesPct	–	selling fees deducted from the comp (default 13, eBay's ~final value fee)
maxItems	–	total listings to score (default 25)

Example

{
  "source": "craigslist",
  "query": ["nintendo switch"],
  "location": "newyork",
  "feesPct": 13,
  "maxItems": 25
}

How the match works

The eBay comps are fetched once per search and each marketplace listing is matched — by title tokens, weighting model/capacity numbers ("13", "128gb", "oled") — to the subset of comps describing the same good. So a single "nintendo switch" search correctly benchmarks an OLED console against OLED comps and a Joy-Con pair against Joy-Con comps, without a separate eBay lookup per listing. Prices in a different currency than the comp are converted with a static, approximate FX rate and flagged fxApplied.

Pricing

All-in pricing — platform usage (proxies, compute) is included, no API key, no separate proxy bill. Per-search summary rows are free.

Event	Price	When
Actor start	$0.001	Flat, once per run
eBay comps fetched	$0.025	Once per search whose eBay comp set was obtained (never when eBay was blocked or empty)
Listing scored	$2.00 per 1,000	Per marketplace listing delivered, scored or explicitly unscored

The comp fetch is one fixed lookup per search whatever maxItems is, so scoring 25 listings costs about the same as scoring 5; set maxItems to what you will actually read.

Notes

• Not affiliated with eBay, Craigslist or Subito. Respect each site's terms.
• Asking-price comps are an estimate of resale value, not a guarantee; sold comps (with your cookie) are the realistic figure.