A marketplace app with a margin guard,
not just a buy button
We are building our own marketplace, so we already know where a marketplace app actually breaks. A seller listing below cost without noticing. An order the fulfillment side cannot actually deliver. A catalogue that drifts out of sync between app and backend. We build the guards for those first and the storefront second.
What it is and who it’s for
A marketplace app connects buyers and sellers, or suppliers, inside one mobile product. It handles search, listings, checkout, payment splitting and fulfillment on both sides.
It’s for a business building a two-sided platform: physical goods, services, or digital goods like keys, subscriptions and in-game currency. Margin discipline and catalogue integrity matter here as much as the storefront design.
We build this category differently because we are building one ourselves. ProBay is the digital goods marketplace we are launching, and it has already taught us where marketplace apps fail quietly. Usually in pricing and fulfillment, long before anyone notices in the UI.
What’s inside the app
The buyer side covers search, categories, cart and checkout with local payment methods. The seller side, whether a full app or an in-app cabinet, covers listing management, order fulfillment and payout visibility. Sellers never have to guess when they get paid.
Underneath both sits a pricing engine with a margin floor that accounts for platform fees automatically. A listing can’t go live priced below what the platform needs to survive. That’s a rule we verified in a pre-launch run against 864 orders, with zero sold below cost.
Catalogue sync from suppliers or sellers includes deduplication. A marketplace with the same product listed five different ways under five different sellers is a search and trust problem waiting to surface. Order and fulfillment guards catch a sold item the supply side cannot actually deliver before it becomes a refund dispute. Payment splitting handles the platform’s commission against each seller’s payout automatically.
We also build in the operational detail that protects a marketplace once real sellers and buyers are on it. A dispute and refund workflow keeps evidence attached to the order, rather than resolved over chat with no record. A seller rating system actually affects search ranking, so quality gets rewarded. Rate limits on supplier APIs keep a pricing sync job from accidentally getting your own integration banned by a provider. Search and category structure are built to scale past the first few hundred listings. A taxonomy that works for a small catalogue often breaks down awkwardly once it grows by an order of magnitude.
How we build it
- Build the pricing engine before the storefront. Margin floors and fee logic protect the business. The UI can wait a sprint. The margin floor cannot.
- Normalize the catalogue from day one. Deduplication and category structure, built in rather than cleaned up after launch.
- Add fulfillment guards at the order step. Catching an undeliverable order before it is confirmed costs far less than a refund dispute after.
- Build seller tools that reduce support load. A seller who can see their own payouts and fulfillment status files fewer tickets.
- Launch with commission reporting visible. The economics of the platform should be checkable from day one, not reconstructed later from scattered data.
Price and timeline
| Tier | Price | What’s included | Timeline |
|---|---|---|---|
| MVP | from $10,000 | Buyer app, seller cabinet, pricing engine with margin floor, basic checkout | 8 to 14 weeks |
| Production | from $18,000 | MVP plus payment splitting, fulfillment guards, admin commission reporting | 14 to 18 weeks |
| Full control, handover-ready | from $19,000 | Everything in Production plus full handover documentation for your own team | 14 to 18 weeks |
What you own at the end
The catalogue, the pricing engine’s rules, and the order and payout data, all under your own database and infrastructure. Payment processing runs through your own provider accounts, not a dependency on us. The repository is yours on payment, as set in the contract, with read access from day one.
Related
See the e-commerce service page for how we approach marketplaces and stores end to end. The e-commerce mobile app and on-demand services app pages cover adjacent two-sided builds. For infrastructure, see b2b wholesale portal price lists and split payments and payouts. For the real numbers behind this engine, see ProBay, the marketplace we are launching and digital goods marketplace automation.
Building a marketplace and worried about sellers listing below cost or orders you cannot fulfill? Get in touch and we will show you the guards first.
FAQ
How much does a marketplace app cost?
From $10,000 for a buyer and seller app with a pricing engine and margin floor. Multi-seller payment splitting, dispute handling and catalogue deduplication at scale typically run $15,000 to $25,000.
How long does it take?
8 to 14 weeks depending mostly on catalogue complexity and whether payment splitting between sellers is in scope. A single-category marketplace ships faster than a multi-vendor platform with variants and sub-orders.
What stops sellers from listing below cost or getting double-booked?
A pricing engine with a hard margin floor that accounts for platform fees before any listing goes live. It's the same logic we built for our own marketplace, where a pre-launch verification run checked 864 orders and found zero sold below cost. Inventory and fulfillment checks catch the double-booking problem at the order step, not after.
Who owns the marketplace, the code and the data?
You. The repository, the catalogue, and the order and payout data live under your own infrastructure. Payment processing runs through your own Stripe, crypto gateway or local provider account, not ours.
Can this handle digital goods specifically, like keys or subscriptions?
Yes, we have built exactly this. Automated delivery guards, supplier integrations with best-price selection, and a margin-floor pricing engine for a large, multi-currency catalogue. It runs in client projects and in the marketplace we are launching ourselves.