Marketplace: Complete Definition and Guide

What is a Marketplace?

A marketplace, or online marketplace, is a multi-sided digital platform that connects at least two groups of users: sellers (or service providers) and buyers (or clients). The marketplace typically does not own the products or services sold; it provides the technological infrastructure, trust, and visibility necessary for transactions to take place. Its business model primarily relies on commissions taken from each transaction, sometimes supplemented by subscriptions, listing fees, or premium services.

This model has revolutionized many sectors: Amazon and eBay for physical commerce, Airbnb for accommodation, Uber for transportation, and Upwork for freelancing. Each of these platforms created a market by reducing friction between supply and demand. In Belgium and across Europe, the marketplace market is experiencing sustained growth, with local players addressing specific needs in food, personal services, and industry.

At KERN-IT, we have direct experience developing marketplace-type platforms. We notably built Spentys, an order management platform for medical 3D printing that operates on a marketplace model, connecting medical practitioners, 3D designers, and printing centers. This experience confronted us with the specific technical challenges of this type of platform: multi-actor management, complex payment flows, commission systems, and approval workflows.

Why Marketplaces Matter

The marketplace model has established itself as one of the most powerful digital business models because it creates value for all stakeholders while benefiting from considerable network effects.

• Network effects: the more sellers there are, the more buyers the platform attracts, which in turn attracts more sellers. This virtuous cycle creates a natural barrier to entry for competitors and exponential growth in platform value.
• Model scalability: unlike a traditional business that must manage inventory, a marketplace can grow without proportionally increasing its operational costs. The technical infrastructure evolves, but the model remains asset-light.
• Centralized trust: the marketplace acts as a trusted third party by managing payments, customer reviews, disputes, and guarantees. This intermediation reduces risk for buyers and facilitates market access for small sellers.
• Data and intelligence: the platform centralizes valuable data on purchasing behavior, market trends, and seller performance. This data enables optimizing user experience and making informed strategic decisions.
• Market fragmentation: many sectors remain fragmented with suppliers and buyers struggling to find each other. A marketplace creates value by solving this discovery and matching problem.

How It Works

A marketplace relies on several interconnected technical building blocks. The core of the system is the matching engine, which allows sellers to publish their offerings and buyers to search, filter, and compare them. This engine typically relies on an advanced search system (Elasticsearch or PostgreSQL full-text) to deliver relevant and fast results.

The payment system is the most complex and critical element. In a marketplace, money flows from a buyer to the platform, which takes its commission, then transfers the balance to the seller. This payment splitting mechanism requires a specialized payment provider like Stripe Connect or Mollie Connect, capable of managing connected accounts, deferred payments, and automatic commissions. In Europe, the PSD2 directive imposes strict compliance requirements, including Strong Customer Authentication (SCA) for online payments.

The user management system distinguishes several roles: buyers, sellers, administrators, and sometimes intermediate roles such as moderators or delivery agents. Each role has specific permissions and tailored interfaces. The seller dashboard displays orders, revenue, and statistics, while the admin back-office handles moderation, disputes, and the platform's global metrics.

Order workflows define the transaction lifecycle: from initial order to delivery, through seller confirmation, payment, shipping, and buyer validation. Webhooks play a central role in this orchestration, notifying the platform of payment events (successful payment, refund, dispute) and triggering appropriate actions.

Real-World Example

One of KERN-IT's most representative projects in the marketplace domain is Spentys, an order management platform for the medical 3D printing sector. Spentys connects practitioners (orthopedists, surgeons) who order custom medical devices, with designers who create 3D models, and printing centers that manufacture them.

The main technical challenge was managing a complex multi-actor workflow: the practitioner initiates the order with a patient 3D scan, the designer creates the model, the practitioner validates it, the printing center manufactures the piece, and the practitioner confirms receipt. At each stage, the system manages notifications, validations, and status updates. Payment occurs at different moments depending on the order type, with commissions dynamically calculated based on volumes and product types.

This project illustrates the difference between a generic SaaS marketplace (Sharetribe, Arcadier) and a custom platform. The business workflows specific to the medical sector, compliance requirements, and complex payment flows could not be handled by an off-the-shelf solution. Custom development in Python/Django allowed us to precisely meet the client's needs while ensuring the solution's scalability and maintainability.

Implementation

1. Define the multi-sided model: clearly identify user groups (sellers, buyers, providers) and the value the marketplace creates for each. Define the revenue model: fixed commission, percentage, subscription, freemium, or hybrid.
2. Design payment flows: choose a payment provider that supports payment splitting (Stripe Connect, Mollie Connect). Implement connected accounts for sellers, KYC (identity verification), and automatic commission management. Ensure PSD2 and SCA compliance for the European market.
3. Develop the search engine: implement advanced search with filters, sorting, and facets. For large catalogs, integrate Elasticsearch for optimal performance. For smaller projects, PostgreSQL's full-text search is often sufficient.
4. Build workflows: model the order lifecycle with states, transitions, and conditions. Use webhooks to synchronize payment events with order status. Implement notifications (email, push) at each key stage.
5. Manage trust: implement a rating and review system, an offer moderation process, a dispute resolution mechanism, and buyer guarantees. These elements are essential for reaching the critical mass of users.
6. Deploy and scale: containerize the application with Docker for easy deployment. Set up performance monitoring, alerts on failed transactions, and business metrics (GMV, conversion rate, average order value).

Associated Technologies and Tools

• Django: Python framework ideal for marketplaces thanks to its powerful ORM, authentication system, and built-in admin.
• Stripe Connect / Mollie Connect: payment providers specialized in marketplaces, handling payment splitting, KYC, and PSD2 compliance.
• Elasticsearch: distributed search engine for large catalogs with full-text search, filters, and facets.
• React: JavaScript framework for building reactive user interfaces and dynamic seller dashboards.
• PostgreSQL: relational database for managing complex relationships between users, products, orders, and payments.
• Celery: asynchronous task system for processing payment webhooks, sending emails, and generating reports.

Conclusion

Building a marketplace is a technical and strategic challenge that goes far beyond simply creating an e-commerce site. Multi-actor management, commission-based payment flows, trust systems, and complex workflows require specific expertise in custom development. SaaS marketplace solutions (Sharetribe, Mirakl) work for standard cases, but projects with specific business workflows — like Spentys, which we developed at KERN-IT — benefit from a custom approach in Python/Django. Our experience developing these platforms enables us to support Belgian companies looking to create their own marketplace, from business model design to production deployment, including payment system integration and monitoring tool setup.