Guestimator: What's It Worth?

Snap it, get a price from live eBay listings, and list it on your own eBay account. NVIDIA Nemotron on Nebius Token Factory does the reasoning.

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Inspiration

Everyone who has cleared out a garage or a relative's house asks the same question: what is this worth? Answering it takes an hour of searching listings and squinting at maker's marks, and then you still have to write the eBay listing. We wanted to photograph the thing and be done.

30-second tour (new look + the no-cut Guestimator Market): https://youtube.com/shorts/aL_T2E7ChFk . The video above is the full walkthrough.

Latest (Oct 7): the Guestimator Market terms are live (we take no cut; sellers agree once). Every photo slot has Camera and Upload buttons. Sellers can enter size and weight, so a 5-foot cabinet is compared with full-size pieces, not tabletop ones. A brand painted on an object, or sitting next to it in the photo, is no longer taken as its maker. Price ranges stay within the listings actually kept as comparables, and the research robot plays a full 76-second loop so a long wait never looks frozen.

What it does

Photograph an item from a few angles and type what you know. Guestimator identifies it and prices it from what comparable items are listed for on eBay right now and what they actually sold for in the last 90 days, and shows those listings so you can check the number. It shows what it read off the label and which listings it set aside, and why. When two identifications are plausible it asks you instead of guessing. For signed art and maker pieces it also looks up the maker's other work at auction.

Then one tap writes the eBay listing: category from eBay's taxonomy, item specifics restricted to eBay's allowed values, only conditions that category accepts, photos, description and a price from the comparables. You review every field, and it publishes to your own eBay account. Two real listings were made this way on Sep 27, 2026 (eBay items 198671504189 and 198671529701).

Since the first submission it has also become a place to sell, not just a way to list on eBay:

  • Guestimator Market (app.theguestimator.com/market): put a priced item in your own shop with one tap. Buyers pay you directly through your own Stripe account. Guestimator takes no cut.
  • Garage and estate sale pages with QR price tags, hold requests and online checkout.
  • Shipping: box size and weight estimated from the photos, live carrier quotes, and labels.
  • Share your price: a public page for any estimate, with an invite link.
  • When an item sells anywhere, its other listings come down, so nothing sells twice.

Judges: sign up at https://app.theguestimator.com. New accounts start with 5 free credits; for 10 more, tap the credits pill at the top and enter 10FREECREDITS under "Have a code?" (one credit = one estimate or one eBay listing).

How we built it: NVIDIA Nemotron on Nebius Token Factory

Every estimate runs on Nebius Token Factory, called straight from a Cloudflare Worker through its OpenAI-compatible endpoint. There is no GPU server of our own.

  • Gemma 3 27B (MiniCPM-V 4.5 as fallback) reads each photo on its own: labels, marks, part numbers.
  • NVIDIA Nemotron 3 Super (nvidia/nemotron-3-super-120b-a12b) does the reasoning. It gets one evidence sheet (the photo reads, the owner's notes, which outrank the model, live eBay listings, recent eBay sales and web results) and returns JSON: what the item is, how sure it is, the price, and which listings don't match. It also checks for silver and gold (melt value becomes a floor), re-prices against the evidence it kept, writes the listing title and description, and fills eBay item specifics.
  • The searches (eBay listings, eBay sold prices via SoldComps, a Tavily web search and the maker lookup) run in parallel, and the listing copy is written after the price is shown. Recent estimates take about 45 to 55 seconds, down from about 70.
  • A Cloudflare Queue runs one estimate per invocation; D1 holds items and a credits ledger; R2 holds photos.
  • Listings go through eBay's Sell Inventory, Taxonomy, Metadata and Account APIs on the user's own account (OAuth, refresh tokens sealed with AES-GCM).
  • Market and sale checkouts are Stripe Connect direct charges on the seller's own account, with no platform fee.
  • Credits are sold through RevenueCat (Google Play Billing on Android, RevenueCat Web Billing on the web).
  • 1,570 automated checks, with eBay, Stripe and the models stubbed at the network layer.

Challenges we ran into

Reasoning tokens. Nemotron 3 Super thinks inside the same completion budget as its answer, so a small max_tokens can be used up before any JSON appears. Every call now asks for at least 6,000.

The empty price. One re-price came back as the model's own blank template, all zeros, and a truthiness check accepted it. The Worker now tests that a price is actually usable and warns instead of ever showing a silent $0.

eBay categories are not uniform. Some categories take no condition at all; sending one fails at publish time. Conditions now come from each category's own list.

Speed. The first version did each search one after another and wrote the listing before showing the price. Running the searches side by side and writing the listing afterwards cut about 20 seconds.

Accomplishments that we're proud of

Real prices on real objects: an 1878-patent cast-iron fluting iron identified as Shepard Hardware Co. of Buffalo ($120-250), server memory priced from four live eBay listings, and two real eBay listings published through the app.

What we learned

Give the reasoning model one well-built evidence sheet instead of a conversation, let the owner's own words outrank the model, and make it say which evidence it threw out. That is what makes the number checkable.

What's next for Guestimator

Etsy cross-listing (built, waiting on Etsy's app approval), an iOS app, and growing the Market.

Built With

  • android
  • capacitor
  • cloudflare-d1
  • cloudflare-queues
  • cloudflare-r2
  • cloudflare-workers
  • ebay-api
  • gemma
  • javascript
  • minicpm-v
  • nebius
  • nebius-token-factory
  • nvidia-nemotron
  • revenuecat
  • shippo
  • soldcomps
  • stripe-connect
  • tavily
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