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Sold-price comps API for resale marketplaces

Build a sold-price/comps API and pricing tool for resale marketplaces (Poshmark, Mercari, Depop) aimed at resellers, cross-listing tools, and inventory/pricing apps that need clean historical sold data now that eBay locked its sold listings behind login. Monetize via API subscriptions, a Google Sheets add-on, and a fee calculator for resellers pricing items across platforms.

via Hacker News
Original post

What to build

A sold-price comps API for secondhand clothing on Poshmark, Mercari, and Depop, aimed at resellers and the cross-listing/inventory tools (List Perfectly, Vendoo-style apps) that need pricing data now that eBay hid its sold listings behind a login wall. Ship it as a REST API with a Google Sheets add-on and a simple web lookup tool for individual resellers.

eBay locking sold-listing data behind login has created a gap for third-party sold-price data on resale platforms, and SoldStack's Show HN launch is an early signal that developers are willing to build (and possibly pay) for this.

Demand

Resellers and the makers of cross-listing/inventory tools need comps data to price secondhand clothing, and eBay's login wall removed their default free source — but demand is evidenced by only one small launch so far, not by established paying customers.

  • Hacker NewsLaunch

    Show HN: SoldStack – sold prices API for secondhand clothes — 8 points, 9 comments.

  • SoldStack (product positioning)Product

    Product framed as a response to eBay locking sold listings behind a login, creating demand for alternative sold-price data sources for resellers and cross-listing tools.

Stack

  • Python/FastAPI for the API layer
  • Playwright or Scrapy for data collection
  • PostgreSQL for storing historical sold listings
  • Google Apps Script for the Sheets add-on
  • Stripe for API subscription billing
  • Vercel or Fly.io for hosting

Solo + AI difficulty

The API and billing layer are straightforward for a solo builder with AI help and could be an MVP in 1-2 weeks; the hard, ongoing part is reliably scraping sold-price data from Poshmark/Mercari/Depop without breaking ToS or getting blocked, plus keeping the dataset fresh as marketplaces change their HTML/anti-bot measures. Expect scraper maintenance to be the real long-term cost, not the initial build.

Entry threshold
Low capital barrier, but moderate build effort: requires scraping and continuously cleaning noisy marketplace data (filtering sizes, bundles, duplicates, outliers), plus ongoing maintenance as platforms change their HTML/anti-scraping measures.
Window
6-12 months

Where to find first users

  • Show HN / Product Hunt launch
  • Reseller communities on Reddit (r/Poshmark, r/Flipping, r/Mercari)
  • Outreach to existing cross-listing tool makers (List Perfectly, Vendoo) as a B2B data supplier
  • Facebook groups and Discord servers for resale sellers

Competitors

Counter-signals & risks

  • No historical match found for this opportunity, indicating it is an unproven niche with uncertain market size and willingness to pay.

  • Scraping or aggregating sold-price data from Poshmark, Mercari, Depop, and eBay may violate their terms of service or trigger the same kind of access lockdown eBay itself just imposed.

  • Low moat and high competition risk: existing cross-listing tools or the marketplaces themselves could add native comps features, undercutting a standalone API business.

Original title: Show HN: SoldStack – sold prices API for secondhand clothes

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Sold-price comps API for resale marketplaces — Nichr