Mercury vs Relay: Banking for a B2B Marketplace or Brokerage

The single most important structural decision here is keeping funds that belong to sellers, held briefly before payout, entirely separate from the marketplace's own commission revenue. Confirm with your own counsel and accountant whether your specific transaction flow creates any money transmission or escrow-like regulatory obligations, since that answer varies by how funds actually move and can meaningfully change what account structure and compliance steps you need, beyond what any bank feature alone provides.

Once the regulatory picture is clear, route buyer payments into a dedicated payout account that exists specifically to fund seller disbursements, and let only your confirmed commission move into the marketplace's own operating account, ideally on a schedule tied to when a transaction is fully settled rather than the moment a buyer's payment clears. Relay's free sub-accounts make this separation simple to set up; Mercury's account structure supports it too, with an API that a marketplace running its own transaction platform can use to reconcile payouts against the platform's own ledger automatically.

A payout account handling many transactions needs more frequent reconciliation than a typical operating account, since a discrepancy here means money that belongs to a specific seller is unaccounted for, not just a bookkeeping error to catch at month end. Build daily or near-daily reconciliation into your operations from the start, matching buyer payments in against seller payouts out and your platform's own transaction ledger, so an error surfaces within a day rather than compounding across weeks of transaction volume.

Whatever the current effective federal funds rate of 3.63%¹ makes idle cash worth earning, that consideration applies strictly to the marketplace's own confirmed commission revenue, never to funds awaiting payout to a seller. Mercury's automated Treasury sweep is a reasonable tool for a healthy operating reserve built from the marketplace's own earned commission, but sweeping transaction pass-through funds into any yield product, even briefly, blurs a line that needs to stay bright and clear both operationally and, depending on your specific structure, potentially legally.

A marketplace investing ahead of transaction volume, building sales capacity or platform features before commission revenue catches up, sometimes needs a credit line to bridge the gap. That credit is priced off the bank prime rate, currently 6.75%², and should be sized and serviced entirely against the marketplace's own operating cash and confirmed commission revenue, never against the payout account, which needs to remain fully available to sellers regardless of how the marketplace's own financing situation is going.

A venture-backed marketplace should track the same capital efficiency discipline any growth-stage company does: keep your burn multiple, net burn against net new commission revenue, under 2x³ as a working ceiling. Marketplace economics can be deceptive here, since gross transaction volume looks large while the marketplace's own real revenue is just the commission slice, and burn discipline needs to be measured against that real revenue number, not the larger pass-through volume flowing through the account.

A marketplace running its own transaction and payout platform gets real value from Mercury's API, reconciling bank-side payouts against platform-side transaction records automatically rather than by hand. A smaller marketplace still processing transactions more manually is usually better served starting with Relay's simpler, free sub-account structure, at least until transaction volume justifies the investment in a dedicated platform and the API integration that goes with it.

When a buyer disputes a transaction after a seller has already been paid out, the marketplace needs a clear, documented process for how that's resolved, whether through a reserve held back from future payouts, a direct claim against the seller, or the marketplace absorbing the loss under its own policy. Decide this policy before volume grows large enough that disputes become routine rather than rare, and hold a small dispute reserve inside the payout account structure if your policy calls for one, rather than discovering there's no clear process the first time a meaningful dispute actually happens.

Before finalizing either account, confirm your regulatory obligations around fund transmission with counsel, decide your seller payout timeline and document it clearly, and build a daily reconciliation habit from the very first transaction, rather than waiting until volume is high enough that catching up on weeks of unreconciled activity becomes a real project.

A documented dispute process should settle these questions:

• Whether the marketplace holds back a reserve from future seller payouts to cover disputes that arrive after a seller has already been paid.
• When the marketplace makes a direct claim against the seller instead of absorbing the loss itself.
• Who owns each dispute from the buyer's complaint through resolution, so cases do not stall between teams.
• How the outcome is recorded in the payout account, so money belonging to a specific seller is never left unaccounted for.