Buying a manufacturer is a capital-asset deal as much as an earnings deal. The machines, the building, the inventory, and the people who know how to run the line are the business, and each carries risks that don't show up in a clean P&L. This is a practical manufacturing due diligence checklist: what to verify before you close, and the industrial-specific red flags that should make you slow down. It builds on the general M&A due diligence checklist and the small business acquisition due diligence checklist with the items unique to a plant.
Quick answer: in manufacturing (or factory) due diligence, verify five things before price: the real condition of the equipment and the capex due in the next one to three years, true capacity and the order book, customer and supplier concentration, the quality of inventory and work-in-process, and environmental and safety exposure. Tie every claim to a document or to something you saw on the floor.
The checklist at a glance
| Area | What to request | How to verify | Red flag |
|---|---|---|---|
| Equipment and facility | Fixed-asset register, maintenance logs, capex plan, lease | Walk the floor and match serial numbers to the register | Major replacement due just after close |
| Capacity | Production reports, shift patterns, OEE data, backlog | Compare output claims with shipments and invoices | Plant already near 95% with no capex budgeted |
| Customers | Top-20 customer list, supply agreements, price escalators | Read change-of-control and termination clauses | One customer at 40% or more of revenue |
| Suppliers | Purchase history, single-source list, supply contracts | Ask what happens to pricing on a change of control | Critical input from one supplier, no backup |
| Inventory and WIP | Aged inventory by category, count procedures | Attend or test a physical count | Obsolete stock carried at full value |
| Tooling and IP | Tooling list with owner, drawings, product specs | Confirm who owns each mould, die and fixture | Customer-owned tooling treated as an asset |
| Labor and safety | Org chart, union agreements, OSHA logs, comp mod | Interview supervisors, read incident history | Key know-how held by one person |
| Environment and permits | Phase I/II reports, permits, waste records | Check permit transfer rules and site history | Seller vague about past site use |
| Quality | ISO or sector certificates, audit reports, returns | Read recent customer audit findings | Rising returns or warranty claims |
| Systems | ERP/MRP, costing method, OT network | Rebuild one product's cost from the system | Margins that only exist in a spreadsheet |
What makes manufacturing diligence different
Three things: capital intensity (deferred maintenance and looming capex can swamp the earnings), operational complexity (real capacity and throughput are hard to see from financials), and environmental and safety exposure (liabilities that can follow the asset regardless of deal structure). Most manufacturing surprises after close come from one of those three.
1. Equipment, machinery, and facilities
- ✓Fixed-asset register vs. reality, walk the floor and tie major equipment to the asset list. Note age, condition, and remaining useful life.
- ✓Deferred maintenance and capex, what's been postponed, and what major replacement or upgrade is due in the next 1-3 years? Underfunded capex is a hidden price increase.
- ✓Maintenance records, well-kept logs signal a disciplined operation; their absence is itself a flag.
- ✓The facility, owned or leased, condition, and whether the lease (and any change-of-control terms) transfers.
2. Capacity and throughput
- ✓True capacity utilization, are you buying a plant running at 50% (room to grow) or 95% (capex needed to grow)? This drives the whole growth thesis.
- ✓Bottlenecks and OEE, overall equipment effectiveness and where the line actually constrains.
- ✓Backlog and order book, committed orders vs. an empty pipeline dressed up as steady revenue.
3. Customer and revenue concentration
- ✓Customer concentration, common and dangerous in manufacturing. A single OEM customer at 40%+ of revenue is an existential risk if they re-shore or re-bid.
- ✓Contracts and pricing, long-term supply agreements, pricing/escalator clauses, and change-of-control provisions.
- ✓Quote-to-win and margins by product line, which lines actually make money after full absorption costing.
4. Supply chain and raw materials
- ✓Supplier concentration, single-source suppliers for critical inputs, and what happens to pricing or availability on a change of control.
- ✓Raw-material exposure, sensitivity to commodity prices, and whether the business can pass increases through.
- ✓Lead times and tariffs, dependence on a single region or imported input subject to tariff swings.
5. Inventory and working capital
- ✓Inventory composition, raw materials, work-in-process, and finished goods, each valued and aged. WIP is the easiest to overstate.
- ✓Obsolete and slow-moving stock, is dead inventory padded into the sale value?
- ✓Working-capital cycle, cash tied up between paying suppliers and getting paid. Manufacturers are working-capital heavy; underestimating this squeezes buyers right after close.
6. Labor and workforce
- ✓Skilled-labor dependency, which roles are hard to replace, and how tight is the local labor market?
- ✓Union status, collective bargaining agreements, their terms, and renewal timing.
- ✓Safety record, OSHA history, incident rates, and workers' comp experience modifier (a high mod rate signals real cost and culture issues).
- ✓Key-person knowledge, the floor supervisor who knows the old machine's quirks is a single point of failure.
7. Environmental, permits, and quality
- ✓Environmental liabilities, historical site use, hazardous materials, and any Phase I/II assessment. Some environmental liability follows the asset regardless of deal structure.
- ✓Permits and licenses, air, water, and waste permits, and whether they transfer.
- ✓Quality certifications, ISO 9001, AS9100, IATF 16949, or industry equivalents, plus customer audit history.
8. Tooling, engineering, and product liability
- ✓Tooling ownership, moulds, dies, jigs and fixtures are often owned by the customer, not the plant. Get a tooling list with the owner of each item, and never pay for tooling the business only holds.
- ✓Drawings, specifications and IP, who owns the product designs, and are they documented well enough to run without the current engineers?
- ✓Engineering capability, the engineering due diligence question is whether the team can quote, design and industrialise new parts, or only run existing ones.
- ✓Warranty and product liability, claim history, open recalls, insurance coverage, and any customer contracts that push liability onto the manufacturer.
9. Systems, costing, and the data behind the margins
- ✓ERP and MRP, which system runs orders, inventory and production, and how much of it lives in spreadsheets outside it.
- ✓Standard costing, how product costs are built, and whether the margins by product line survive a full allocation of overhead.
- ✓OT and cybersecurity, machines connected to the network, remote access for vendors, and backups for the programs that run the equipment. A ransomware outage on the line stops shipments.
The factory site visit: what to look at on the floor
A factory due diligence visit tells you things no data room will. Plan it, do not treat it as a tour.
- ✓Walk the full route of one order, from goods-in through each process step to shipping, and note where material waits.
- ✓Look at the machines that are not running, and ask why. Idle equipment is either spare capacity or broken capacity.
- ✓Check housekeeping and safety, guarding, marked walkways, chemical storage and spill kits say a lot about how the plant is run.
- ✓Match what you see to the asset register, a sample of serial numbers is enough to test it.
- ✓Talk to the supervisors, not only the owner, ask what breaks most often and what they would buy first.
- ✓Look at the building, roof, floor slab, power supply, and room to expand if your plan needs it.
Document request list for a manufacturing acquisition
Ask for these early, so the review runs in parallel with the site visits:
- ✓Three to five years of financial statements, plus monthly management accounts for the last 24 months.
- ✓Fixed-asset register, maintenance logs, and the capex history and plan.
- ✓Production, capacity and OEE reports, and the current backlog.
- ✓Top customer list with revenue by customer, and every supply agreement.
- ✓Supplier list with spend, and the single-source items.
- ✓Aged inventory by raw materials, WIP and finished goods, and the last count results.
- ✓Tooling list with ownership, product drawings and specifications.
- ✓Organisation chart, employment and union agreements, OSHA logs and workers' comp history.
- ✓Environmental reports, permits and waste records.
- ✓Quality certificates, recent customer audits, returns and warranty claims.
- ✓Real estate deeds or leases, insurance policies, and any litigation.
Manufacturing-specific red flags
- ✓Equipment running on borrowed time with a big capex bill looming just past close.
- ✓A single OEM customer at 40%+ of revenue, especially with re-shoring pressure.
- ✓Single-source suppliers for critical inputs with no backup.
- ✓WIP or finished-goods inventory valued optimistically, with obsolete stock buried in it.
- ✓A high workers' comp experience mod or a poor OSHA record.
- ✓Environmental history the seller is vague about.
- ✓Tooling that turns out to belong to customers, or drawings that exist only in one engineer's head.
- ✓Product margins that cannot be rebuilt from the costing system.
Where the time goes, and how to compress it
Most manufacturing diligence is reading and reconciling: the fixed-asset register, maintenance logs, supply agreements, customer contracts, inventory reports, environmental assessments, and a data room of PDFs, cross-checking each claim against the document. It's slow and detail-heavy, and the costliest items (deferred capex, obsolete inventory, a key supply contract) are the easiest to gloss over.
This is the part you can systematize. Deal OS reads the documents in a deal workspace and produces source-cited diligence briefs and findings, every claim quoted from your own documents and verified before you see it, plus risk, contradiction, and missing-information audits across the room. It doesn't replace the floor walk, your equipment appraiser, or your environmental advisor; it gets you to the questions that matter faster. See how we approach diligence automation for the document-heavy review. If a standard workspace doesn't match how you work, the same approach can be delivered as custom AI development for founders grounded in your own documents, and buyers reconciling this paperwork deal after deal often turn it into AI automation across multiple entities.
Frequently asked questions
What is the most important thing to check when buying a manufacturing business? Real capacity and the condition of the equipment. A plant running near full capacity needs capex to grow, and deferred maintenance is a hidden price increase. Tie the fixed-asset register to a physical floor walk, and budget the capex due in the next one to three years before you agree a price.
How do you value inventory in a manufacturing acquisition? Separate raw materials, work-in-process, and finished goods, and value and age each. WIP is the easiest to overstate. Identify obsolete or slow-moving stock and confirm it isn't padded into the sale value, and verify the physical count rather than trusting the report.
What are the biggest red flags in a manufacturing acquisition? Looming capex on worn equipment, a single OEM customer at 40%+ of revenue, single-source suppliers for critical inputs, optimistically valued or obsolete inventory, a poor safety/workers'-comp record, and environmental history the seller won't detail.
What documents should I request in manufacturing due diligence? Financial statements and monthly accounts, the fixed-asset register and maintenance logs, capex history and plan, production and backlog reports, customer and supplier contracts, aged inventory, the tooling list with owners, labor and safety records, environmental reports and permits, quality certificates, and leases and insurance. The full list is above.
What should you look at during a factory site visit? Follow one order through the plant from goods-in to shipping, ask why idle machines are idle, check safety and housekeeping, match a sample of serial numbers to the asset register, talk to supervisors about what breaks, and inspect the building, power supply and room to expand.
Who owns the tooling in a manufacturing business? Often not the business. Moulds, dies and fixtures are frequently paid for and owned by the customer and only held at the plant. Get a tooling list that names the owner of each item, and make sure customer-owned tooling is not counted as an asset in the price.
Can AI help with manufacturing due diligence? Yes, for the document-heavy parts. Tools like Deal OS read the supply agreements, customer contracts, asset registers, and data-room documents and produce source-cited findings and contradiction audits, so you reach the real questions faster. It supports your diligence; it doesn't replace the floor walk, an equipment appraisal, or professional advisors.
Review your next industrial deal with less grind
If reconciling the asset register and reading the supply contracts is eating your nights, see an example of how Deal OS turns a workspace of documents into cited diligence findings.
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