The Weekly Supplier Invoice Audit Checklist
- Michael Intravartolo
- 8 hours ago
- 4 min read
If we want to stop margin leak, we need a process we can run every week, even when we are slammed.
This checklist is built for trade businesses that process high line-item supplier invoices and cannot afford to “spot check and hope.” If we do this consistently, we catch the small errors that repeat and quietly add up.
If you want the bigger picture on how these issues compound over time, start here: Supplier Invoice Errors: How Trade Businesses Lose Margin Without Knowing It.
Why weekly audits beat random spot checks
Supplier invoice errors rarely show up as one big obvious mistake. They show up as patterns.
That is also why ERPs and approvals do not reliably protect us here. They help invoices move through the process, but they are not designed to validate supplier pricing behavior over time. This explains the blind spot in plain terms: Why ERP Systems Don’t Catch Supplier Invoice Errors.
Weekly audits win because they create two things most teams do not have:
A consistent baseline
A consistent standard for what gets flagged
What we audit first
If we only have 30 minutes, we focus on what repeats. Repeat items and repeat fees create the biggest exposure.
1) Repeat items by spend
Start with the top 20 to 50 items we buy most often.
2) Repeat suppliers
Focus on the suppliers that show up on invoices every week.
3) Repeat fees
Freight, fuel, handling, processing, compliance. These often drift because they “feel normal.”
For a quick list of the most common line-item traps (and what they look like), use this as your reference post: 9 Supplier Invoice Traps: The Truth About Line Items.
The Weekly Supplier Invoice Audit Checklist
Use this checklist in order. It is designed to catch issues fast without turning invoice review into a full-time job.
Check 1) Unit price drift
What to do: Compare this week’s unit prices on repeat items against the last 3 to 6 invoices.
What you are looking for: Small increases that repeat without a clear reason.
Check 2) Unit of measure changes
What to do: Confirm the unit of measure matches what we normally buy (each vs box, feet vs roll).
What you are looking for: A UOM swap that changes the extended cost.
Check 3) Pack size changes
What to do: Confirm pack quantity and effective per-unit price.
What you are looking for: “Looks close” pricing that is actually worse per unit.
Check 4) Duplicate lines that do not look duplicated
What to do: Scan for near-duplicate descriptions, repeated part numbers, and split quantities.
What you are looking for: A second charge that blends in.
Check 5) Fee creep
What to do: Compare freight, fuel, handling, and misc fees against last month.
What you are looking for: Fees that slowly rise or suddenly appear and then never leave.
Check 6) Substitution overbilling
What to do: When an item is substituted, compare the replacement price to what was originally ordered.
What you are looking for: A “stock issue” that quietly becomes a higher bill.
Check 7) Early price increases
What to do: If we received a price notice, verify the effective date matches the invoice date.
What you are looking for: Increases applied early or inconsistently.
Check 8) Job-coded misc charges
What to do: Review misc charge categories that get coded straight to jobs.
What you are looking for: Charges that bypass scrutiny because they are “part of the job.”
Check 9) Supplier pattern recap
What to do: Track which suppliers generate the most flags.
What you are looking for: Repeat behavior, not one-off noise.
How to run this in 30 minutes
Pull this week’s supplier invoices.
Choose the top 2 suppliers by volume.
Choose the top 20 repeat items by spend.
Compare against the last 3 invoices for those items.
Flag exceptions and send them for confirmation before payment.
If we want a seasonal example of how fast drift can show up during busy periods, these posts show it clearly:
When it makes sense to automate the checklist
If we are doing this every week and still feel behind, it is usually because:
invoice volume is too high
line items are too dense
pricing changes too often
we do not have time to compare history across suppliers
That is the point where automation stops being “nice to have” and becomes the only scalable way to catch patterns consistently. Here is the walkthrough of how 3rd Armor approaches it: How 3rd Armor Works.
Proof this approach works in the real world
When this becomes consistent, results show up fast because we are no longer relying on memory and spot checks.
Two examples worth reading:
Next step
If we want to tighten margin protection quickly, the simplest move is to start running this checklist weekly on repeat items and repeat suppliers.
If you want to see what this looks like using your invoices, start here: Contact 3rd Armor
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