3PL Warehouse Site Audit Checklist: Inventory, Safety and Billing

The quarterly business review went well. The 3PL showed 99.8% inventory accuracy, zero lost-time injuries and an invoice dispute rate under 1%. Two months later, a customer order shorts on a lot the client's ERP says is in stock, the warehouse finds 36 cartons were written off by a night-shift adjustment nobody approved, and the CCTV that might have explained it has already been overwritten.

Scorecards reported by the 3PL measure what the 3PL chooses to count. A client-side site audit tests the same claims independently: a blind count against the warehouse ledger, a walk through the safety and security records, and a re-performance of recent invoices from activity data. Done with a written evidence request, named owners and fixed timing, a two-day visit can surface the variances that monthly reports smooth over.

• What follows: the evidence to request two weeks ahead, how to sample and count, where adjustments and damage hide losses, the safety and security checks, and a billing re-performance with worked US ($) and India (₹) invoices.
• Tools you can reuse: a stratified sampling query, an adjustment-trail incident trace, a split of fixed checks versus assisted review, and a dated audit checklist with owners.

What a client audit of a 3PL site has to prove

A site audit has three jobs: confirm your goods exist, are yours and are segregated; confirm the site is not putting people or stock at avoidable risk; and confirm the invoices match the work done. Anything that does not serve one of those three questions belongs in the business review, not the audit.

Many 3PLs offer an assurance report in place of a visit. A SOC 1 Type 2 report tests the design and operating effectiveness of the provider's controls over a period, and auditors of your financial statements may rely on it. It is valuable evidence, but it describes the provider's control system across all clients; it does not count your SKUs, read your adjustment log or recalculate your invoices.

A SOC 1 Type 2 report issued under AICPA AT-C section 320, or a Type 2 report under ICAI SAE 3402 in India, tests a 3PL's controls over a period but never counts the depositor's SKUs; a client site audit still needs a blind count of at least 60 locations against the WMS stock ledger.

Legal context frames the stakes. Under UCC Section 7-204(a), a US warehouse is liable for loss or damage caused by failing to take the care a reasonably careful person would take, and Section 7-204(b) lets the storage agreement cap that liability. The audit should therefore compare the contractual cap and the 3PL's insurance with the value of stock you actually hold there.

The evidence request letter sent fourteen days before the visit

Send a written evidence request fourteen days ahead, naming each document, the period it must cover and who at the 3PL will supply it. Asking for records on the day turns the audit into a search; asking in writing lets you test what arrives and spend site time on what does not reconcile.

Fix the stock cut-off in the letter: for example, the WMS stock-on-hand extract as of 23:59 on the day before the visit, by location, SKU, lot, expiry and status. Ask for the same period for every activity record so the counts, adjustments and invoices can be tied to each other rather than to three different months.

Blind counts and trace tests on the warehouse floor

Count blind, in both directions, and before picking starts. Counters get a list of locations with no quantities; system-to-floor tests prove booked stock exists, and floor-to-system tests catch stock sitting in locations the WMS thinks are empty or assigned to another client.

Sixty locations is a practical minimum for a mid-size account, stratified so fast movers, high-value items, lot-controlled items and every location touched by a recent adjustment are over-represented. A purely random sample drawn across tens of thousands of positions mostly lands on slow, untouched stock and tells you little about where losses occur.

-- Stratified blind-count sample for one depositor, drawn from the WMS stock extract
-- Strata: A movers 20, high value 15, lot/expiry controlled 10, adjusted in 90 days 15
WITH soh AS (
  SELECT location_id, sku, lot, qty, unit_value, velocity_class, lot_controlled
  FROM   wms_stock_on_hand
  WHERE  owner_id = 'CL-0417' AND snapshot_ts = '2026-10-13 23:59:59'
),
adj AS (
  SELECT DISTINCT location_id FROM wms_inventory_adjustment
  WHERE  owner_id = 'CL-0417' AND posted_ts >= DATE '2026-07-15'
)
SELECT * FROM (SELECT *, 'A_MOVER'  AS stratum, ROW_NUMBER() OVER (ORDER BY RANDOM()) rn FROM soh WHERE velocity_class = 'A') a WHERE rn <= 20
UNION ALL
SELECT * FROM (SELECT *, 'HIGH_VAL' AS stratum, ROW_NUMBER() OVER (ORDER BY qty * unit_value DESC) rn FROM soh) h WHERE rn <= 15
UNION ALL
SELECT * FROM (SELECT *, 'LOT_EXP'  AS stratum, ROW_NUMBER() OVER (ORDER BY RANDOM()) rn FROM soh WHERE lot_controlled) l WHERE rn <= 10
UNION ALL
SELECT * FROM (SELECT s.*, 'ADJUSTED' AS stratum, ROW_NUMBER() OVER (ORDER BY RANDOM()) rn FROM soh s JOIN adj USING (location_id)) j WHERE rn <= 15;

-- Scoring after the count
-- location_accuracy = locations where SKU, lot and quantity all match / locations counted
-- value_variance    = sum(abs(counted_qty - system_qty) * unit_value) / sum(system_qty * unit_value)
-- Pass: location_accuracy >= contract target (example 99.5%) AND value_variance <= 0.2%

Score both measures separately. A site can hit 99% location accuracy and still lose meaningful value if the misses are on expensive items, which is why the value variance sits beside the count. Unit-level accuracy should be reported too, but never instead of location accuracy, because offsetting overs and shorts hide in a unit total.

Segregation is part of the count. In shared buildings, check that each counted pallet carries your owner code on its label and in the WMS, and that no other client's stock shares the location record. Our guide to keeping customer-owned stock separate covers the location and label rules to look for.

Adjustments, damages and quarantine: where stock leaves quietly

Most shrink at a 3PL does not walk out of the door; it is written off in the WMS through adjustments, damage postings and quarantine moves that nobody on the client side approved. The adjustment log is therefore the most productive single document in the evidence pack.

Read it by user, by aisle and by time of day. Clusters of negative adjustments by one user, on one aisle, on a night shift, or immediately before month-end are the pattern to chase. Every write-off above the agreed threshold should carry a client approval reference; one that does not is a contract breach before it is a stock question.

1. 21:47, 12 September: WMS transaction ADJ-NEG posts −36 cartons of SKU 88412, lot B2607, at location C-14-03, reason code CNT-VAR, user NS-SUP-03; the approval reference field is blank.
2. 23:59, 30 September: the month-end stock file sent to the client omits the 36 cartons; the client ERP still holds them, and a 36-carton difference enters the reconciliation as "timing".
3. 10:20, 14 October: the audit blind count finds location C-14-03 empty; the CCTV retention setting is 30 days, so footage for 12 September was overwritten on 12 October.
4. 10:55, 14 October: the auditor filters the adjustment log and finds 14 negative adjustments by the same user on aisle C in 60 days, all between 21:00 and 23:30, none with an approval reference.
5. Corrective control: the WMS now blocks negative adjustments above 5 cartons or $500 without a client approval ticket, and CCTV retention on high-value aisles is raised to 90 days.

Damage and quarantine deserve the same scrutiny. Ask for photos and the damage report behind each item, check the age of anything sitting in quarantine, and confirm who carries the loss under the storage agreement. Differences that persist between your ERP and the 3PL's stock report are analysed in our article on why 3PL stock reports and ERP balances disagree.

Safety walk: lift trucks, racking, fire protection and exits

Test the safety system through its records first and the floor second. A clean-looking aisle tells you little; an expired operator evaluation or a missing monthly extinguisher check tells you the controls behind the aisle are not working.

In the US, OSHA's powered industrial truck standard sets checkable dates. Operators need a performance evaluation at least once every three years, the employer must certify each operator's training and evaluation with names and dates, and trucks must be examined before being placed in service at least daily, or after each shift where used round the clock. Portable extinguishers need a monthly visual inspection and an annual maintenance check.

A 3PL safety walk should test the training file against OSHA 29 CFR 1910.178(l)(4)(iii), which requires every powered industrial truck operator to be evaluated at least once every three years, and 1910.178(q)(7), which requires trucks to be examined at least daily before use, so any pre-shift checklist older than 24 hours fails.

• Operator file sample: pick ten operators from the shift roster, not from the training file, and find a certificate with an evaluation date inside three years for each.
• Truck checklist: match today's pre-shift checklists to truck numbers in use on the floor at 10:00.
• Racking condition: look for bent uprights, missing beam locks and load signs that do not match the pallets stored; ask for the last rack inspection report and its open items.
• Fire and egress: check extinguisher tags for the monthly initials and annual service date, sprinkler heads clear of stored goods, and exits unobstructed.

In India, the Occupational Safety, Health and Working Conditions Code, 2020 has been in force since 21 November 2025 and replaced the Factories Act, 1948 among other laws. Ask which registrations and licences the 3PL holds for the site under the Code and state rules, and for its fire service clearance where the state requires one. Our guide to warehouse safety inspections that lead to corrective decisions covers how to turn findings into closed actions.

Security and custody records that protect client stock

Security checks should prove that stock only leaves against a valid order and that every trailer can be traced from gate to dock to seal. The documents are the gate log, the seal register, the CCTV configuration and the access list for any high-value cage.

Trace five outbound shipments from the client order to the WMS pick confirmation, the dispatch document, the seal number and the gate-out time. Then trace five inbound receipts the other way. Gaps between gate-out time and the WMS ship confirmation of more than an hour, or seals recorded after the trailer left, are findings even if no stock is missing.

Indian warehouse operators must keep records of consignor, consignee, storage period, dispatch and receipt under CGST Section 35(2) and Rule 58(4)(b), and Rule 58(5) requires goods to be stored so they are identifiable item-wise and owner-wise; an auditor should trace 20 inward documents to owner-tagged locations.

For India, also confirm the address on your GST registration covers the 3PL site where you store goods there, that the 3PL either is registered or holds a GST enrolment under Rule 58(1), and that e-way bills for transfers into and out of the site match the WMS receipts and dispatches by date and quantity.

Re-performing three months of invoices from activity data

Billing is audited by rebuilding the invoice from WMS activity and the rate schedule in force, not by checking arithmetic on the invoice itself. Rebuild the last three months; one month can be a coincidence, three show whether a variance is systematic.

Use the method the contract specifies for each charge. Storage may be billed on daily pallet-days, a month-end snapshot or a peak count; the rules for each are explained in our article on pallet-day storage billing. That article sets out how a storage charge should be calculated; this audit tests whether the 3PL actually applied the agreed method to your account.

The US variance comes almost entirely from the storage clock, which is typical: storage is the largest line and the easiest to measure on the wrong basis. In India, the excess includes ₹5,580 of GST, so the correction should come as a credit note that reduces both the taxable value and the tax, rather than as a deduction from the next payment that leaves the GST return and your credit claim out of step.

Fixed audit checks versus reviewer judgement and tool support

Checks with a precise rule, such as a count matching the ledger or an evaluation date inside three years, should be run the same way at every site. Software, including AI tools, earns its place in reading images and spotting patterns in long logs, but a named auditor decides what counts as a finding.

Dated audit checklist, finding grades and closure deadlines

Run the audit to a calendar: request at minus fourteen days, desk review at minus five, site work over one or two days, draft findings within ten working days, and corrective actions closed or re-tested before the next quarterly review. Grade every finding so the 3PL knows which ones block contract renewal.

Grade findings in three bands: critical (stock or safety exposure, fix within 7 days), major (control failure, fix within 30 days) and minor (documentation gap, fix by next audit). More guides on warehouse control and 3PL management are in our logistics and supply chain hub. If you want the count sampling, adjustment analytics and invoice rebuild automated from your 3PL's data feeds, send us a request for proposal describing your sites and billing terms.