Build a marketplace app with AI — two-sided by default

A marketplace is two apps in one — a buyer flow and a seller flow — sharing a single backend. Both need to ship in V1 or you do not have a marketplace, you have a catalogue.

Buyer flow: search and category browsing, listing detail with photos and seller profile, in-app messaging with the seller, Stripe Connect checkout (so the platform fee splits automatically), and an order history with a dispute path. The buyer side is what investors and customers see first, but it is meaningless without the seller side.

Seller flow: create-and-manage listings with photo upload and pricing, an inbox for buyer conversations, an order fulfillment view, and a payout dashboard backed by Stripe Connect. If sellers cannot self-serve from day one, you are operating a manual concierge service, not a marketplace.

In-app messaging: real-time WebSocket-backed chat between buyer and seller, with per-listing threads and unread counts. Email-only is a non-starter — both sides expect chat, and the message log is the audit trail when a dispute lands.

Reviews and trust: post-transaction reviews (both directions), seller verification stub, and visible ratings on listings. Trust is the moat in a marketplace; the review system is what builds it.

Stripe Connect (not regular Stripe): the difference is enormous. Regular Stripe means you are a merchant of record; Stripe Connect splits the payment between platform and seller automatically and handles seller onboarding (KYC, payout setup). Get this right in V1 — migrating later is painful.

Three mistakes that kill marketplaces before they reach liquidity.

Building only the buyer side first. Founders think "I'll add seller tools after I get demand" and then realise sellers will not onboard via email-and-CSV. By the time the seller flow exists, the buyers have lost interest. AppGenie ships both flows in the first pipeline run — keep them, even if you are seeding supply manually for the first month.

Skipping in-app messaging. Sellers need to answer questions before a sale; buyers need to coordinate logistics after one. Punt this and the deals happen on Instagram DMs instead of your platform — you lose the audit trail, the trust signals, and (eventually) the transaction itself when both sides realise they can deal off-platform.

Treating Stripe Connect as "just Stripe." Stripe Connect requires seller onboarding (KYC, payout method, country compliance) and a different webhook flow than a normal Stripe checkout. Founders wire normal Stripe in V1, then need a two-week refactor to add seller payouts. AppGenie scaffolds Stripe Connect from the first prompt; do not downgrade it.

Traditional timeline: four to six months for a small team to build buyer flow, seller flow, listings, search, messaging, Stripe Connect payouts, and a review system. Agency cost: $100,000 to $300,000 — marketplaces are at the top end because of the two-sided complexity, the messaging system, and the Stripe Connect compliance work.

With AppGenie: the buyer flow, seller flow, listings, search, in-app messaging, Stripe Connect, and reviews generate in the first pipeline run — typically three to five minutes for the first live preview. The output is a full Expo + React Native codebase that runs on iOS, Android, and web from the same source, with role-based navigation and the WebSocket messaging plumbed end-to-end.

What this means in practice: you spend your first month on the chicken-and-egg problem (seeding supply, finding the first buyers) — the real reason most marketplaces fail — instead of building listing pages and chat infrastructure for the third time this decade.

The ongoing cost is your AppGenie subscription plus your backend hosting and Stripe Connect fees. No agency retainer, no platform-takes-30% lock-in.