Carrier Invoice Audit: Are You Overpaying on Shipping?
Wuunder has been processing resell rates for carriers for over 10 years. Based on that experience, we see that 2-5% of all carrier invoices contain errors, particularly in surcharges. At 2,500 shipments per month averaging €8 each, that's €400-1,000 per month in unjustified costs. Per year: €4,800-12,000 you're unknowingly overpaying.
Most e-commerce businesses don't systematically check their invoices. Too complex, too time-consuming, and there's no reference point to compare against. With the right tools, you do have that reference point: the rates you receive via the Wuunder API when booking are your benchmark for verifying invoices afterwards. In this article, we explain where errors hide, how to budget shipping costs upfront, and how to verify your carrier's invoice.
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The base rate is just the beginning
A carrier invoice is more than just the base rate. On top come up to 11 cost layers: road toll per country, fuel surcharges (monthly or weekly variable), peak surcharges, out of area surcharges, extra handling, exceeding maximum size surcharges, insurance, parcel shop/locker discounts, not home/not collected surcharges, and hidden costs from quality and performance. Each layer can differ per carrier, per route and per month. Read the full breakdown at Compare shipping costs.
It's precisely these layers on top of the base rate where most invoice errors occur. Below are the 9 most common.
The 9 most common invoice errors
1. Weight correction
Weight surcharges are often unjustified. The most common cause: a carrier employee places two parcels on the belt at the same time instead of one, doubling the recorded weight. Many carriers therefore measure and weigh twice: at the receiving sorting centre and at last mile. If they only weigh once, the risk of errors is high. Always check whether the billed weight is realistic for the item in question. Use the dimensions and weight you submitted to the carrier when booking the shipment as your reference. Via the Wuunder API you can easily retrieve this booking data per shipment and compare it against the invoice.
2. Volume correction (recalculation)
Carriers measure the dimensions of every parcel at their sorting centre. If the measured dimensions are larger than what you stated and that difference pushes your shipment into a higher rate bracket, a recalculation charge follows. The same applies to weight: you only get a surcharge when the difference crosses a tariff threshold. Use PuzzlPack to help warehouse staff pack orders in the right box, so your stated values always match. Also watch packaging quality: when dozens of kilos are stacked on top of a parcel in a roll container, weaker boxes can bulge outward. A box that fits within standard dimensions suddenly measures as oversized. Always make sure packaging can't bend open under pressure. Bonus: by systematically checking invoices for volume corrections, you also discover if staff are consistently using oversized packaging, or if your PMS contains incorrect dimensions or weights for certain items. Invoice auditing becomes a warehouse and product data optimisation tool.
Volume corrections also directly impact your checkout pricing. If you charge a flat €5 shipping fee for every product but consistently receive €10 in surcharges, that €5 is too low and you're losing margin. By using PuzzlPack in the checkout, you can pass on near-exact shipping costs per order. This is especially crucial for international express shipments by air: every gram and centimetre costs significant money. If you don't pass on the real costs, your margin drops or you have to lower conversion with inflated flat shipping fees.
3. Fuel surcharge discrepancy
Fuel surcharges fluctuate monthly (sometimes weekly). Check whether the percentage on your invoice matches the carrier's published percentage for that month. With a 20% fuel surcharge and 1,000 shipments per day averaging €8, a 1 percentage point discrepancy costs around €80 per day, or over €1,600 per month.
4. Residential surcharge on business addresses
Express carriers like DHL Express, UPS and FedEx charge residential surcharges on home addresses. Problem: sometimes business addresses in residential areas are incorrectly flagged as residential.
5. Duplicate billing
Some carriers invoice the same shipment multiple times. On top of that, shipments that were cancelled or returned still appear on the invoice. Especially hard to detect at high volumes with multiple carriers. Filter on tracking numbers that appear more than once and compare cancelled bookings against your invoice.
6. SLA violations without compensation
With express services, carriers guarantee a delivery time (e.g. "before 12:00 next business day"). If that promise isn't met, you often have the right to a discount or credit. Most businesses don't claim this. Via Wuunder Track you can see exactly when a shipment was delivered and automatically flag SLA breaches.
7. Undelivered shipments returned without attempt
A common issue: a shipment is returned without the carrier ever attempting delivery at the recipient's address or dropping it off at a parcel shop. Or the carrier makes only one delivery attempt when two were agreed in the contract. By comparing your tracking data and booking data (including expected shipping costs) with the invoice, you catch these immediately. If a parcel shop scan is missing from the tracking, or only one delivery attempt is registered when two were agreed, your administration should automatically file a claim. Wuunder Track gives you the tracking data to prove it.
8. Incorrect tariff on the invoice
You agree on €4.00 per shipment in your contract, but the invoice shows €4.40. This happens more often than you'd think, especially with new contracts. The same applies to surcharges: the agreed surcharge rates don't match what's being invoiced. Check the first invoices of every new contract line by line and keep doing this periodically. The rates you receive via the Wuunder API when booking are your benchmark.
9. Import duties charged back to the retailer
For international shipments outside the EU, the carrier collects import duties from the recipient. If that fails, the duties are charged back to you as the retailer. How this works in practice differs per carrier: some carriers deliver to the door and collect duties on the spot. Others bring the shipment to a parcel shop where the recipient must pay before receiving the parcel. The latter is a worse customer experience: your buyer expects home delivery but now has to visit a pick-up point and pay first. Check your invoice for charged-back import duties and how often this occurs per carrier. A high percentage of charged-back duties says something not just about your invoice, but about the service you offer your buyer. Choose your carrier partly based on how they handle import duties. More on customs and import duties at international shipping.
Checklist: how to audit your carrier invoice
- Compare billed weight with your stated values: check if the weight is realistic for the item, and whether two parcels may have been weighed together
- Compare billed volume with your stated values: spot-check whether the dimensional weight on the invoice matches your booking data
- Verify the fuel surcharge: compare the percentage with the carrier's published surcharge for that month
- Search for duplicate shipments: filter on tracking numbers that appear multiple times
- Claim late deliveries: File claims within the agreed timeframe
- Check undelivered returns: compare tracking data with the invoice. If a parcel shop scan is missing or only one delivery attempt is registered when two were agreed, file a claim immediately
- Compare rates with your contract: verify that the invoiced base rate and surcharges match your contract terms, especially with new contracts
- Check oversize/overweight surcharges: spot-measure your parcels and compare with the invoice
- Monitor charged-back import duties: check if you're being charged import duties that should have been collected from the recipient, and compare the rate per carrier
The booking data generated when requesting a shipping label from the carrier is the same data you use to verify invoices. Read more about the label process.
Prevention vs. correction: two approaches
Correction after the fact (audit model)
Some platforms offer AI-powered tools that check carrier invoices after the fact and recover errors. Typical checks include: shipment validity, duplicate billing, delivery/SLA, billed weight/volume, tariff price, surcharges, and a dispute workflow. This model is reactive: you overpay first and try to recover afterwards. Moreover, such a system needs to have shipped and invoiced 120,000 different services before it knows what something should cost. And even then, the question remains whether what the carrier invoiced previously was correct in the first place. In effect, you're only checking whether a carrier invoices the same amount again, not whether the rate is right.
Proactive: book right and verify afterwards
Wuunder combines both: book correctly upfront, then verify against hard data. Based on your contract with the carrier, we build a rate and service overview. This can amount to 120,000+ carrier services with all rates, surcharges and capability data. When you book a shipment, you receive the expected rate including virtually all surcharges via the API. Those rates are your reference point: use them to budget shipping costs and to verify your carrier's invoice afterwards.
Specifically:
- Rates per shipment via the API: every booking returns the expected rate including fuel surcharge and volume and/or weight surcharge. This is your reference for invoice verification
- Budget shipping costs upfront: use the API rates to more accurately forecast your shipping spend before you ship
- Connect your own contract: you see your contract rates in the platform and can verify per shipment whether the invoice is correct
- PuzzlPack: calculates exact packaging dimensions upfront so there's no discrepancy between stated and measured values
- Real-time carrier data: surcharges are updated as soon as you sign a new contract with the carrier or the carrier adjusts its rates
Discover the possibilities
We'd love to show you during a demo how Wuunder transforms your daily workflow.
Q: How often do carrier invoices contain errors?
A: Based on over 10 years of processing resell rates, Wuunder sees that 2-5% of all invoice lines contain errors, particularly in surcharges. At high volumes this quickly adds up to thousands of euros per year.
Q: Which surcharges are most often incorrectly billed?
A: Volume correction (oversized or deformed packaging, incorrect PMS data) and weight correction (two parcels weighed together) are the biggest error sources, followed by incorrect contract rates and duplicate billing of the same shipment.
Q: Does Wuunder offer an invoice audit tool?
A: Wuunder takes a proactive approach: book correctly upfront and verify afterwards. Every booking returns the expected shipping rate via the API, including virtually all surcharges. Those rates are your reference for verifying your carrier invoice. PuzzlPack additionally prevents dimensional weight discrepancies. By importing these rates into your ERP system, you can easily identify differences with the carrier's transport invoice.
Q: Can I compare my carrier invoice with Wuunder data?
A: Yes. The rates you receive via the API when booking are your benchmark. Connect your own transport contract and you compare per shipment what the platform calculated vs. what the carrier invoiced.
Q: How do I claim SLA violations from my carrier?
A: We share the track & trace data of every shipment via Wuunder Track, allowing you to easily run your own analyses. We can of course also help you set this up. File your claim within the term stated in your contract. For express carriers this is typically 14-30 days.