Marketplace buying and selling between people's agents

Selling a used bike or sofa online is mostly logistics and haggling: is it still available, what condition is it in, will you take less, when can I pick it up. A seller’s agent and a buyer’s agent could settle all of that in a minute. What stands in the way today is less the technology than the platforms’ terms, the lack of any verified identity between strangers, and the scams that thrive in this channel.

How it works today

People list items on general marketplaces and classified sites, then trade messages with buyers. Payment happens in person or by transfer, and the item changes hands at a meetup.

Platform terms. The big consumer venues do not invite software to take part. Meta’s terms (section 3.2) bar accessing or collecting data from its products by automated means without prior permission. craigslist’s terms bar collecting content with robots, scripts or scrapers, and bar software other than its own app and general-purpose browsers and email clients from interacting with the site without a separate licence.

Scams. The FTC describes the overpayment pattern: a buyer sends a check for more than the price and asks for the difference back. Banks must make deposited funds available quickly, so the money appears before the check is found to be fake, and the seller repays the bank weeks later.

Rules for sellers and platforms.

• In the US, the INFORM Consumers Act, in effect since 27 June 2023, requires online marketplaces to collect and verify bank, tax ID and contact details from high-volume third-party sellers: 200 or more sales of new or unused consumer products and $5,000 or more in gross revenue in a 12-month period. Sellers with $20,000 or more a year must have their name, address and contact details disclosed to buyers. The FTC and state attorneys general enforce it.
• The IRS says payment apps and online marketplaces report on Form 1099-K when payments for goods or services exceed $20,000 in more than 200 transactions, and that selling personal items at a gain is reportable income.
• In Canada, Part XX of the Income Tax Act has required reporting platform operators, since 1 January 2024, to collect, verify and report information on reportable sellers, including name, address, date of birth where applicable, tax identification number, financial account identifiers, and the amounts paid to the seller. Returns and seller copies are due by 31 January of the following year.

The agent-to-agent version

Illustrative. This assumes a venue that lets agents take part, or sellers who publish their own agent endpoint. A buyer’s agent makes an offer on a listed bike:

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "SendMessage",
  "params": {
    "message": {
      "role": "ROLE_USER",
      "messageId": "msg-mk-2208",
      "parts": [
        {"text": "Is the road bike still available? My principal offers 380 CAD, pickup this Saturday."},
        {
          "data": {
            "listingRef": "listing-51093",
            "offer": {"amount": "380.00", "currency": "CAD"},
            "questions": ["frameSize", "serialNumber", "knownIssues"],
            "pickupWindows": [{"start": "2026-10-03T14:00:00Z", "end": "2026-10-03T18:00:00Z"}],
            "payment": "transfer at pickup after inspection"
          },
          "mediaType": "application/json"
        }
      ]
    }
  }
}

1. The seller’s agent answers the questions from the listing and the seller’s notes, including the serial number so the buyer can check it before meeting.
2. The seller’s floor is 400. The agent counters at 400 and moves the task to TASK_STATE_INPUT_REQUIRED.
3. The buyer’s cap allows 400. It accepts, and both agents confirm a public meetup spot and time.
4. Each agent sends its owner a summary: price, item details as stated, time and place, and payment method. The inspection, the handover and the payment stay with the two people.

What has to be true

Identity. Strangers have no shared identity layer. INFORM verification applies only to high-volume sellers of new or unused goods, so a private seller of a used bike is unverified. An agent’s identity, even a verified one, proves who built and runs the agent, not that the person behind it is honest.

Authority. Each owner sets a price floor or ceiling, acceptable payment methods and whether the agent may commit to a meetup. Some rules should be absolute: never send money back from a payment, never move to a payment method the owner did not approve, never share verification codes.

Record. Today the marketplace’s message thread is the record. An agent exchange should leave both owners the same summary of what was agreed, including the condition claims, since those are what a later dispute turns on.

Safety. Agents read messages and listings written by strangers. Any text in a listing is untrusted input and can carry instructions aimed at the other agent.

Where Emissar fits

Person-to-person marketplaces are not Emissar’s starting market, and Emissar cannot change a platform’s terms. If venues open to agents, some modules would apply:

• Verify (in development) would tell each side which provider runs the other agent and whether it has a history of abuse.
• Mandate (spec in progress) would carry the owner’s limits, such as the price range and payment methods.
• Ledger (spec in progress) would give both owners a signed copy of the agreed terms.

Open questions

• Permission. Will the major venues publish agent interfaces, or keep treating software as a terms violation?
• Off-platform risk. Moving a deal to direct agent-to-agent contact can take it outside the venue’s buyer protections and fraud monitoring.
• Scale abuse. Agents make it cheap to send hundreds of lowball offers or scam openers. Rate limits and reputation have to exist on both sides.
• The meetup. Inspection, handover and personal safety are physical. Agents can arrange them but should not pretend to manage them.