Payments · Guide · 7 min read
The merchant acquirer fee audit: a practical guide for finance leaders
A merchant acquirer fee audit is a line-by-line reconciliation of card processing charges against your contracted pricing, published interchange rates and card scheme fee schedules. It identifies billing errors, unannounced margin changes and transactions charged at the wrong rate.
- Who this is for
- CFOs, finance directors and payments leads at organisations that accept cards at volume.
- Why it matters
- Acquirer pricing combines interchange, scheme fees and acquirer margin. Each layer changes on its own schedule, and summary statements rarely separate them clearly. Over a multi-year contract, small differences compound quietly.
Executive summary
- 1Card charges have three layers that must be checked separately.
- 2Most leakage sits in four zones: misqualification, scheme mark-ups, margin drift and fixed fees.
- 3Start with transaction-level files and every pricing notice, not the PDF statement.
Where do acquirer charges drift from what was agreed?
1. Interchange misqualification
Transactions fall into higher-cost interchange categories because data such as card-present indicators or authentication results are missing or incorrect. Warning sign: a rising share of transactions in premium or non-secure categories.
2. Scheme fee mark-ups
Scheme fees described as passed through at cost carry an additional margin, rounding or fee lines that do not match the card scheme's published charges. Warning sign: scheme fee lines that move when the card schemes made no change.
3. Acquirer margin drift
Contracted rates change through general notices, tier resets or expired promotional pricing, without a renegotiation. Warning sign: an effective rate that rises while your card mix stays stable.
4. Terminal and gateway charges
Recurring charges continue for decommissioned terminals, unused gateway features or duplicated services across providers. Warning sign: fixed monthly fees that no longer match your estate.
| Charge layer | Set by | What we verify against | Typical check |
|---|---|---|---|
| Interchange | Card issuer | Published interchange schedules | Correct category per transaction |
| Scheme fees | Visa, Mastercard | Scheme fee circulars | True pass-through at cost |
| Acquirer margin | Acquirer | Your signed pricing schedule | Contracted rate applied |
| Fixed and service fees | Acquirer, gateway | Contract and active estate | Charged only for live services |
How do we run a first review?
- Request the raw files, not the PDF. Ask your acquirer for transaction-level settlement and fee reports in CSV format.
- Gather your contract and every pricing notice received since signing. These define what you should be paying.
- Calculate your effective rate by card type, region and channel, then compare it with your contracted rates.
- Reconcile interchange, scheme fees and acquirer margin separately. A blended view can hide an error in one layer behind savings in another.
Why do manual checks miss things at scale?
A manual review usually samples a few months and a few card types. Low-frequency, high-value discrepancies sit outside that sample.
Sources and methodology
- Card scheme published interchange and scheme fee schedules. Referenced as the verification baseline; no figures are reproduced.
Want an independent view of your acquirer charges?
Share what you process and who with. We will tell you what an audit would examine and what files to gather.
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