Table of Contents
Quick Answer
Use Next.js 15 + Supabase + Stripe Connect for the core, with AI-powered moderation (image + text), fraud scoring, and buyer-seller matching. Handle escrow via Stripe Connect destination charges. Solve the chicken-and-egg by manual seller recruiting first.
- Time to MVP: 3-6 weeks
- Cost: $50-200/mo + 2.9% + 0.25% platform fee to Stripe
- Biggest challenge: Liquidity (solve one side first)
What You'll Need
- Next.js 15, TypeScript, Tailwind
- Supabase (self-hosted) + pgvector
- Stripe Connect (Express accounts)
- AI APIs for moderation & matching
Steps
- Pick a niche. Horizontal marketplaces (Etsy clones) are graveyards. Win with vertical: "marketplace for vintage synthesizers" > "marketplace for music gear."
- Solve one side first. Manually recruit 50 quality sellers before building buyer UX. Without supply, demand doesn't matter.
- Build seller onboarding. Stripe Connect Express account creation. Ask AI: "Generate a Next.js route that creates a Stripe Connect Express account and returns onboarding link."
- Listing flow. Title, description, images, price. AI moderation: scan description + images for prohibited content (drugs, weapons, adult). Use Claude Vision or open-source NSFW detectors.
- Search & discovery. Embed listing text, semantic search via pgvector. Add filters (price range, category, location).
- Buyer checkout. Stripe destination charge routes money to seller minus platform fee. Hold funds in escrow via manual
captureif disputes expected. - AI trust scoring. Score each seller on response time, dispute rate, review sentiment. Flag risky ones automatically.
- Reviews & messaging. Two-way reviews after transaction. In-platform messaging with AI monitoring for scams (off-platform payment requests).
Common Mistakes
- Building supply via ads: Wasted money — recruit sellers manually first.
- No trust & safety: One bad seller kills the vibe. Moderate aggressively.
- Weak disputes process: Buyers need recourse. Automate refund requests with AI triage.
- Hosting all payments: Use Stripe Connect. You're not a payment processor.
- Ignoring SEO: Each listing should be a SEO-indexable page.
Top Tools
| Tool | Best For | Price |
|---|---|---|
| Stripe Connect | Payments | 0.25% + card fees |
| Supabase | DB + auth + realtime | Free tier |
| Algolia-alt (pgvector) | Search | Free |
| Claude Vision | Image moderation | API cost |
| PostHog | Funnel analytics | Free tier |
Conclusion
Marketplaces are hard but defensible. Win a vertical, solve supply first, build trust relentlessly. Stripe Connect + Supabase + AI moderation gives you Airbnb-grade infra for a few hundred a month.