Proof in every line1. A rate that doesn't match the agreement
The most common cause is a rate that changed in one system but not another: a negotiated discount that never reached billing, an old rate still in use after an addendum, or a standard price applied instead of yours. Check: quantity × your agreed rate for each fee, by effective date.
2. Volume tiers applied per line instead of per month
If your agreement lowers the rate after a monthly volume, the discount should apply once total volume passes the threshold. Billing each line at the first-tier rate, or resetting the count each invoice, quietly overcharges busy months.
3. Percentage surcharges on the wrong base
Fuel, peak or handling surcharges are often a percentage of specific fees. If the percentage is calculated on the whole invoice, or on fees it shouldn't include, the surcharge is too high even when the percentage itself is right.
4. Storage counted on the wrong unit or count
Storage may be billed per pallet, shelf, bin or cubic foot. Check the unit matches your agreement and that the count is plausible for the month. A storage line that jumps without a matching change in inventory is worth a question.
5. The same charge twice
Duplicate lines happen when work is re-keyed or a system retries. The same fee, order and amount appearing twice deserves a look, though sometimes the work really was done twice (a repack, for example).
6. Fees on orders you cancelled
If an order was cancelled before it was picked, there should usually be no pick or pack fee. Matching invoice order numbers to your store's cancellations catches these.
7. Fees that aren't in the agreement at all
New fee names appear: "special handling", "account fee", "unlisted surcharge". They aren't proof of an overcharge, but they are worth asking about, especially when they repeat every month.
8. Credits that were promised but never posted
A credit agreed by email is easy to lose. Log each one when it is promised and check later invoices until it appears.
Catching these every month
Each of these checks is mechanical arithmetic, which is why it's tedious by hand and reliable in software. BillProofs runs all eight on every invoice line and shows its working. Run the free check on one invoice to see which apply to you.
Questions
How common are 3PL billing errors?
There is no reliable public figure, and it varies widely by provider and contract. The only way to know for your account is to check your own invoices against your agreement.
Are billing errors usually deliberate?
Usually not. Most come from rate changes that never reached the billing system, manual entry, or tiers and surcharges configured differently from the contract.
What should I send my 3PL?
The invoice lines, the agreed rate with the contract wording, and the difference, grouped by fee and month. Keep it factual and ask for a review.
More guides: How to audit a ShipBob invoice · Common 3PL billing errors · How to dispute a 3PL invoice · 3PL storage fees explained · Spreadsheet vs firm vs software