Who Actually Collects Tax on Your B2B Marketplace

Once your platform meets a state's marketplace facilitator threshold, generally tied to the same economic nexus figures used for direct sellers, you become responsible for calculating, collecting, and remitting sales tax on transactions that happen through your platform, even though the underlying goods or services belong to your sellers, not to you. This shifts a substantial compliance burden onto the platform itself, and it applies per state, which means a marketplace can be a facilitator in some states and not yet in others depending on where its transaction volume has crossed a threshold.

B2B transactions add a wrinkle general marketplace facilitator law was not originally written around: a meaningful share of B2B buyers hold resale or exemption certificates, and a marketplace needs a way to apply those exemptions at the transaction level, not just calculate tax as if every buyer were an end consumer.

If your platform only connects buyers and sellers for negotiation, invoicing, and payment happening off-platform, you may fall outside the facilitator definition entirely in some states, since the statutory tests generally look at whether the platform processes payment and sets terms, not just whether it makes an introduction. A platform evolving from a pure listing service into one that also processes payment should re-check its facilitator status in every state each time that functionality changes, rather than assuming its original classification still holds.

If your marketplace charges sellers a recurring subscription or listing fee separate from transaction-based facilitator obligations, Anrok applies SaaS-style taxability logic to that specific fee and tracks nexus as it grows, while your transaction-level facilitator obligations are tracked through a separate, marketplace-specific process.

For the core facilitator obligation, calculating and remitting tax across thousands of B2B transactions with a meaningful share claiming resale exemptions, Avalara's marketplace-facilitator-specific tooling and certificate management handle both pieces together, which fits a marketplace's actual compliance burden more directly than a subscription-focused tool built for one seller's own revenue.

The prime rate sits at 6.75% as of mid-2026¹, a relevant number for a marketplace financing its own working capital while facilitator tax liabilities sit on the balance sheet between collection and remittance, since that financing cost adds up fast if remittance is ever delayed by a reconciliation problem.

For every state where your platform has meaningful transaction volume, confirm whether you have crossed that state's marketplace facilitator threshold and whether your specific transaction flow, payment processing included or excluded, meets that state's statutory definition of a facilitator. Build a process for re-checking this whenever your platform's payment or invoicing functionality changes, since a feature change can shift your facilitator status in ways a one-time review would miss.

• Platform processes payment and sets transaction terms: facilitator obligations likely apply
• Platform only connects parties, payment happens off-platform: may fall outside facilitator definition, confirm state by state
• B2B buyer holds a resale or exemption certificate: exemption should apply at the transaction level, confirm your platform supports this

A marketplace that launches as a simple listing service and later adds payment processing as a growth feature is the one most likely to miss the moment its facilitator status changed, since the team that built the payment feature is usually focused on conversion and user experience, not on the fact that the same feature quietly shifted a tax obligation onto the platform in every state where it now applies. Treating a payment processing launch as a tax-relevant event, not just a product event, closes this gap.

A second common mistake: assuming a single facilitator determination covers every seller and every transaction type on the platform uniformly, when in practice a marketplace running multiple transaction models, direct sale, auction, RFQ-negotiated deals settled off-platform, may need a different answer for each one.