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Marketplace

// Navigate online marketplaces as buyer, seller, or builder with platform comparison, listing optimization, and scam detection.

$ git log --oneline --stat
stars:1,933
forks:367
updated:March 4, 2026
SKILL.mdreadonly
SKILL.md Frontmatter
nameMarketplace
slugmarketplace
version1.0.1
descriptionNavigate online marketplaces as buyer, seller, or builder with platform comparison, listing optimization, and scam detection.
metadata[object Object]

Architecture

Role-based guidance for marketplace participation. Load relevant file based on user's role.

marketplace/
├── buyer.md      # Price comparison, scam detection, negotiation
├── seller.md     # Listing creation, pricing, platform rules
├── builder.md    # Marketplace creation, economics, liquidity
├── arbitrage.md  # Price gaps, ROI calculations, ToS risks
└── compliance.md # Tax obligations, legal pitfalls, bans

Quick Reference

RoleFileWhen to Load
Buying itemsbuyer.mdComparing prices, spotting scams, negotiating
Selling itemsseller.mdCreating listings, pricing, handling buyers
Building marketplacebuilder.mdDesigning platform, economics, payments
Arbitrage/Resellingarbitrage.mdFinding price gaps, calculating true ROI
Legal/Tax questionscompliance.mdTax nexus, ToS violations, suspensions

Core Rules

1. Platform-Specific, Never Generic

  • Each platform has unique fees, rules, and dynamics
  • eBay auction ≠ Amazon Buy Box ≠ FB Marketplace negotiation
  • ALWAYS specify which platform advice applies to

2. Total Cost, Not Sticker Price

  • Include: platform fees, shipping, taxes, return costs
  • Amazon referral fee varies 8-45% by category
  • eBay 13%+ Poshmark 20%+ Mercari varies

3. Scam Pattern Recognition

  • Stock photos on local marketplaces = red flag
  • "Ship to my address, I'll pay extra" = triangulation fraud
  • Payment outside platform = no protection
  • New account + high-value item + urgency = likely scam

4. Pricing Research = SOLD, Not Listed

  • Listed prices mean nothing—items don't sell at listed price
  • Always research completed/sold listings
  • Factor in condition: "Good" vs "Very Good" = 30% price difference

5. Suspension Risks Are Real

  • Amazon ODR >1% = account death
  • Review manipulation = permanent ban
  • IP complaints from brands = immediate suspension
  • Multiple accounts = instant termination

6. Fee Complexity

Never estimate fees—calculate exactly:

  • Amazon: referral + FBA + storage + return processing + advertising
  • eBay: final value (category-specific) + promoted listings + payment
  • Factor returns into margin (15-30% in some categories)

7. Real-Time Data Required

  • Never quote prices from memory/training data
  • Inventory and pricing change hourly
  • Competitor stock levels affect optimal pricing
  • Always verify current marketplace state before advising