What Is an Online Marketplace? A Guide for B2B Teams

Someone at the board meeting said "we should launch a marketplace." Now you need to understand what that actually means - fast.

An online marketplace is a platform where multiple third-party sellers offer products or services to buyers, while the platform operator manages infrastructure, payments, and rules. Think Amazon or Allegro at the B2C end. At the B2B end: procurement hubs, wholesale platforms, industry-specific supply networks.

This guide explains what an online marketplace is, how it differs from a standard eCommerce store, and - critically - what it means for your tech stack if you're a B2B team considering the model.

What is an online marketplace

A marketplace connects buyers and sellers on a single platform. The operator doesn't own the inventory - it creates conditions for transactions and takes a cut: a commission, a subscription fee, or both.

Three parties are always involved: the platform operator, the seller (vendor), and the buyer. That three-sided model is what separates a marketplace from a regular online store, where a single business owns and sells its own inventory.

The operator sets the rules. Who can sell, what commission structure applies, how disputes are handled, how payments get distributed. The seller manages their own catalog and fulfillment. The buyer sees a unified storefront.

Types of online marketplaces

The marketplace model covers a wide range of formats. The structure varies by who's buying, what's being sold, and how the platform earns.

B2C marketplace

The most familiar format. A single storefront with multiple third-party sellers - Amazon, Allegro, Zalando. Buyers don't always know (or care) which seller they're buying from. Volume and selection drive the model.

B2B marketplace

A procurement or supply platform where businesses buy from other businesses. Examples include industrial supply networks, wholesale platforms, and distributor hubs. The dynamics differ from B2C: longer purchase cycles, invoice-based payments, net-30/60 terms, and approval workflows before orders are placed.

For B2B companies with existing supplier networks, the marketplace model offers a structural shift: you become the hub rather than one of many buyers.

Service marketplace

Platforms connecting buyers with service providers - logistics contractors, maintenance teams, freelancers. The "product" is time or capacity, not a physical SKU. Settlement happens after service delivery, which creates different payment and dispute mechanics than product-based marketplaces.

Hybrid marketplace (1P + 3P)

Retailers like Decathlon or MediaMarkt run both first-party (1P) inventory and third-party (3P) sellers on the same storefront. This creates operational complexity: different return policies, different delivery timelines, different seller quality standards - all visible to the same buyer in a single checkout.

Marketplace vs eCommerce: what's actually different

An online store and a marketplace look similar to the buyer. Under the hood, they're different systems serving different business models.

Revenue model. In a standard eCommerce store, you buy inventory and sell it at a margin. In a marketplace, you earn commission on transactions you never stocked. The financial risk shifts - you don't own the inventory, but you do own the platform and its rules.

Operations. Running a marketplace means running vendor operations: onboarding sellers, auditing catalog quality, managing disputes, splitting orders across multiple fulfillment streams, and distributing payments to multiple parties. None of these processes exist in single-vendor eCommerce.

Architecture. A traditional eCommerce platform is built around one seller, one catalog, one checkout flow. A marketplace requires a multi-tenant data model - every vendor has their own product catalog, their own order stream, their own payout account. That's a fundamentally different architecture, not an extension of what single-vendor platforms do.

When does a marketplace model make sense for B2B?

The marketplace model isn't the right fit for every B2B company. It fits when specific conditions are present.

You have an existing supplier network. If you already work with 20+ suppliers and manage procurement manually, a marketplace platform structures those relationships and automates the operational layer: catalog sync, orders, invoicing, settlement.

Your catalog is too wide to own. Carrying inventory for a 100,000+ SKU assortment means warehouse risk, working capital tied up in stock, and logistics complexity that scales faster than revenue. A marketplace lets you extend assortment without owning it.

You want to become the hub. A B2B marketplace positions you as the central point in your supply chain - the place where your industry transacts. That platform positioning is harder to replicate than product margin.

Your buyer expects a consolidated experience. If enterprise buyers are sourcing from 8 different suppliers, a marketplace gives them a single PO, a single invoice, and a single support contact. That purchasing convenience builds retention.

Why standard eCommerce platforms aren't built for marketplaces

B2B teams typically hit the same wall: the assumption is that existing Shopify or Magento infrastructure can be extended for marketplace functionality. It can't - not without building a second platform alongside the first.

Shopify

Shopify is architected around a single merchant selling their own inventory. Multi-vendor plugins exist, but they're add-ons to a single-merchant foundation. What you get is a workaround:

• No native vendor onboarding with KYC and approval workflows
• No commission engine (percentage splits, tiered structures, category-specific rates)
• No native order splitting - one order from two vendors creates one fulfillment stream, not two separate vendor streams
• No vendor-specific dashboards with order management and payout history
• No settlement layer that distributes payments to multiple parties after a split

The moment multi-vendor operations at scale are needed, you're building custom infrastructure on a platform not designed for it.

Magento

Magento gives you more flexibility than Shopify - open source, extensible, customizable. But building marketplace functionality on Magento means 12-18 months of custom development: a custom vendor portal, custom commission logic, custom settlement, custom catalog isolation per vendor.

Every module you build is technical debt you maintain. Magento doesn't have a concept of "vendor" - you're teaching it. When Magento releases updates, your custom marketplace layer breaks first.

We cover the full breakdown in Why You Shouldn't Build a Marketplace in Magento.

Shopify and Magento were designed for one seller, one catalog, one payout. Adapting them for multi-vendor means building a second platform on top of the first.

What marketplace-specific functionality actually requires

A proper marketplace stack needs capabilities that standard eCommerce platforms don't ship with.

Vendor onboarding and KYC. Sellers don't appear automatically - they register, get verified, and go through an approval flow. That process (identity checks, tax data, bank account verification, contract acceptance) needs to be native to the platform, not bolted on through integrations.

Commission engine. Every marketplace has a revenue model. Whether it's a flat percentage, category-specific rates, tiered structures based on GMV, or subscription-based listing fees - the platform needs to calculate, track, and reconcile commissions across all transactions in real time.

Order splitting. When a buyer orders from three different vendors in one cart, that creates three separate fulfillment streams. The platform needs to split the order, route each part to the right vendor, and track fulfillment independently - while presenting a unified status to the buyer.

Split payments and settlement. Revenue from a single transaction gets distributed between the platform operator and the seller. That requires a settlement layer: holding funds, calculating the split, applying commission, and paying out vendors on a defined schedule.

Dual-interface architecture. A marketplace needs two separate product experiences: a buyer-facing storefront and a vendor-facing dashboard. The vendor dashboard covers product uploads, order management, payout tracking, and performance metrics. These aren't variations of the same UI - they serve completely different workflows.

Marketplace platforms built for this

Standard eCommerce platforms require heavy customization to support marketplace operations. Purpose-built marketplace platforms start from the right architecture. The trade-off is between control, speed, and cost. See the full comparison of multi-vendor marketplace software for a detailed architecture-first breakdown.

SaaS marketplace platforms (Mirakl, Sharetribe)

Fast to deploy, managed infrastructure, no hosting overhead. The cost: enterprise license fees starting around $90,000/year, GMV-based pricing that scales with your transaction volume, and limited ability to customize vendor workflows or business logic outside what the vendor's roadmap allows.

Open Core: Mercur

Mercur is an enterprise-grade Open Core marketplace platform - zero license fees, zero GMV fees, full code ownership.

It ships with the full marketplace stack out-of-the-box: vendor onboarding, commission management, order splitting, split payments, and product catalog per vendor. 80% of marketplace functionality is production-ready from day one. The remaining 20% is customizable for your specific business model - your vendor workflows, your commission structures, your data model - without working around platform constraints.

Deployed across 30+ enterprise commerce projects with $6B+ in client trade volume.

For B2B teams evaluating the architecture: Mercur features and Mercur Enterprise.

Frequently asked questions

What is the difference between an online marketplace and an eCommerce store?

An eCommerce store sells products owned by a single merchant. A marketplace hosts multiple third-party sellers, takes a commission on transactions, and doesn't own the inventory. The platform operator manages the rules, payments, and infrastructure.

Can Shopify be used as a marketplace platform?

Shopify is architected for single-merchant retail. Multi-vendor plugins exist but lack native commission engines, order splitting, and vendor settlement. For production marketplace operations at scale, purpose-built platforms are more practical.

What does a B2B marketplace need that B2C doesn't?

Invoice-based payments (net-30/60), approval workflows for purchase orders, contract pricing per buyer, and more complex onboarding (company verification, tax IDs, credit terms). The B2B buyer journey involves multiple stakeholders and a longer decision cycle.

How long does it take to build a marketplace?

With a purpose-built platform like Mercur (80% out-of-the-box), an MVP marketplace can go live in 4-6 months. Building on top of a general-purpose eCommerce platform typically takes 12-18 months of custom development.

What is an Open Core marketplace platform?

Open Core means the core platform is open source - free to use, modify, and deploy - while enterprise features (advanced integrations, SLA-backed support, hosted infrastructure) are available commercially. Mercur operates on this model: no license fees on the core, commercial options for enterprise requirements.