One canonical catalog. Truthful multi-marketplace execution.
Manage inventory, 4-tier pricing models, cross-channel listing variants, and bounded AI negotiation mandates across eBay, Etsy, Poshmark, Mercari, Depop, Shopify, Facebook Marketplace, OfferUp, and Craigslist. Every connector is fail-closed by default—executing only when certified, authorized, and compliant with marketplace terms.
Canonical Item → Variant Projection
Single source of truth for SKU, photos, condition, and defects. Reconciles sibling variants automatically when an item sells or reserves.
4-Tier Comp-Grounded Price Models
Computes High Anchor, Target, Quick Sale, and Mandate Floor per listing with marketplace fee-adjusted net payout previews.
Fail-Closed API & Guarded Browser
Official APIs for eBay, Etsy, Shopify, and Depop. Isolated Playwright profiles for browser channels that halt on CAPTCHA/MFA challenges.
Authenticated MCP & A2A Mandates
Delegated buyer and seller agents negotiate over JSON-RPC (/api/mcp, /api/a2a) strictly inside signed price floors, budgets, and nonces.
Multi-Marketplace Variant & Mandate Studio
Inspect how a canonical inventory record projects across all 7 featured channels, enforces Etsy 20-year vintage eligibility, and evaluates agent negotiation offers.
1. Select Canonical Inventory Item
minimumUnitPrice)
$1200 USD
2. Inspect Marketplace Variant & Compliance Boundary
eBay Variant Projection
Official API risk: lowPrerequisite: Seller OAuth + Inventory Location + Fulfillment/Payment/Return policy IDs
Channel Compliance Rule: Uses official eBay Inventory API (upsert item -> create offer -> publish) and Notification API with separate Application vs User OAuth token class verification.
3. Test Bounded Agent Negotiation (marketplace.negotiation.offer)
MCP / A2A Policy Check
Truthful 9-Channel Access & Risk Matrix
Every target channel declares 7 granular operations (publish_listing, revise_listing, withdraw_listing, reconcile_listing, fetch_messages, send_message, fetch_offers). Browser automation is never an implicit fallback for official or partner API channels.
| Marketplace | Access Mode | Risk Tier | Default Baseline | Required Activation Artifact |
|---|---|---|---|---|
| eBay | Official API | low | disabled (fail-closed) | Seller OAuth + Inventory Location + Fulfillment/Payment/Return policy IDs |
| Etsy | Official API | low | disabled (fail-closed) | Etsy Open API v3 PKCE OAuth + Handmade/Vintage (>=20 yr) Eligibility Artifact |
| Poshmark | Isolated Browser | high | disabled (fail-closed) | Explicit Owner Browser-Risk Mandate + Persistent Profile Session |
| Mercari | Isolated Browser | high | disabled (fail-closed) | Explicit Owner Browser-Risk Mandate + Persistent Profile Session |
| Depop | Partner API | medium | partner_required (fail-closed) | Signed Partner Approval Artifact + Depop Selling API OAuth Scopes |
| Shopify | Official API | low | disabled (fail-closed) | Shop Domain + Admin GraphQL 2026-07 Token + Publication & Location IDs |
| Facebook Marketplace | Partner API | medium | partner_required (fail-closed) | Signed Meta Partner Artifact OR Separate Owner Browser-Risk Mandate |
| OfferUp | Isolated Browser | high | disabled (fail-closed) | Explicit Owner Browser-Risk Mandate + Local Handoff Policy |
| Craigslist | Isolated Browser | high | disabled (fail-closed) | Explicit Owner Browser-Risk Mandate + Local Handoff Policy |
Cryptographically Bounded Agent Representatives
Personal AI agents connect to nex-listing via authenticated JSON-RPC endpoints. Free-form chat messages can never accept an offer, leak exact pickup addresses, or commit inventory—every commercial transition runs through deterministic canonical operations.
{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "marketplace.negotiation.offer",
"arguments": {
"listingId": "lst_contax_g2_1996",
"expectedVersion": 0,
"idempotencyKey": "offer-2026-10-23-01",
"price": { "amountMinor": 138000, "currency": "USD" },
"quantity": 1
}
}
}