Vendor Fraud: 7 Common Schemes and How to Prevent Them

Most vendor fraud doesn't start with a sophisticated hack or a mastermind scheme. It starts with one invoice that looks completely normal, submitted by a vendor that doesn't actually exist, and nobody catches it because the same person who set up the vendor is the one approving the payment.

This guide covers the seven most common schemes, the red flags worth watching for, and the controls that work without a big finance department.

What is vendor fraud?

Vendor fraud happens when someone inside or outside a company exploits the accounts payable process to steal money. The schemes vary, but they all use AP as the exit door for cash, whether through fake invoices, inflated bills from real vendors, or payment details quietly changed to route funds elsewhere. Most of these schemes are simple, which is exactly why they work so often at growing companies.

The risk is highest when AP teams are lean. If the same person is processing payments, running payroll, and handling close tasks, there's no natural second set of eyes on vendor setup or payment changes. Small leaks can run for months before anyone notices.

Internal vs. external vendor fraud

Internal vendor fraud involves employees who create fake vendors, approve inflated invoices, or divert payments. External vendor fraud comes from outside parties: a real vendor overbilling, competitors rigging bids, or a fraudster impersonating a vendor to redirect payments. The worst cases involve collusion between insiders and outsiders, which is one reason "trust the approver" workflows break down over time.

Why vendor fraud happens

Vendor fraud doesn't require sophisticated hacking. It thrives on everyday gaps in how payments get processed, especially when AP is moving fast with limited review. Smaller companies bear more of the damage because they're more likely to have one person wearing too many hats.

Manual processes and weak onboarding

Fake vendor schemes slip in when onboarding happens without verifying Tax ID, physical address, or business registration. If you're onboarding vendors through email threads and spreadsheets, it's easy to miss a mismatch that a basic checklist would catch. Without a step that cross-checks vendor data against employee records, a shell company can sit in the master file for years.

Lack of segregation of duties

This is the single biggest structural vulnerability at smaller companies. When one person can add a vendor, approve an invoice, and process the payment, there's no checkpoint to catch fraud. Compensating controls like owner review still work if your company is too small for full separation.

High invoice volume

When AP processes a high volume of invoices each month, each one gets less scrutiny. A duplicate submitted soon after the original or a small overbilling on a recurring service blends right into the noise. Round-dollar invoices for vague "consulting" also tend to slip through when volume is high.

7 common vendor fraud schemes

These schemes all exploit the same handful of process gaps, and none of them require deep technical knowledge to pull off.

1. Ghost vendors

An employee creates a fictitious company in the payment system, submits invoices from it, and routes payment to themselves. This can be accomplished with little more than a fake name and a post office box. We watch for P.O. box-only addresses, addresses matching an employee's home, sequential invoice numbers, and round-dollar amounts.

2. Invoice overbilling

A real vendor inflates prices or quantities, often with an internal employee who approves the inflated amounts in exchange for a cut. There's no obvious red flag on any single invoice because the vendor relationship is legitimate. You usually catch this through price checks against market rates or original contract terms.

3. Duplicate invoicing

A fraudster submits the same invoice twice, or a slightly altered version, and diverts the second payment. Small changes to invoice numbers or dates make duplicates harder to spot without automated matching. We've seen cases where an accounting manager made duplicate payments, then had vendors refund the overpayment to an account they controlled.

4. Vendor impersonation and email compromise

A fraudster poses as an existing vendor, typically through spoofed email, and sends updated banking details. The next payment goes straight to the fraudster's account. If you see a "new ACH form attached" email, verify it by calling a phone number from your contract records, not the number in the email.

5. Kickbacks and employee collusion

An internal employee steers contracts to a preferred vendor in exchange for cash or gifts. The vendor inflates invoices to cover the kickback, so the company pays more for everything. These schemes are hard to detect because the vendor is real, the invoices look normal, and the approver is the one benefiting.

6. Check tampering

An employee with access to blank check stock forges signatures or alters payee information to divert payments. This tends to persist when check stock isn't secured, signatures aren't controlled, and bank reconciliation isn't independent. For companies still paying by check for a meaningful slice of vendors, the process needs to be tighter than "the checks are in a drawer."

7. Bid rigging and price fixing

Competing vendors coordinate to manipulate a bidding process so a predetermined vendor wins. One or more vendors submit intentionally high bids or refrain from bidding entirely. This hides behind what looks like a competitive process, so it often only becomes visible when bid patterns are compared over time.

How to detect vendor fraud

Detection is less about fancy tooling and more about reviewing the data you already have. We focus on three places where schemes leave footprints: invoices, the vendor master file, and payment behavior.

Check invoices for red flags

Poor formatting, blurry logos, and personal email addresses (Gmail, Yahoo) on invoices are potential indicators of a fake vendor. Round-dollar amounts are suspicious too, since real vendor bills typically reflect specific quantities and rates. Invoices that consistently land just below approval thresholds are another pattern worth documenting, especially from the same vendor.

Review vendor data for warning signs

We cross-reference the vendor master file against employee records on a regular cadence. Any overlap between vendor addresses and employee home addresses, or between vendor Tax IDs and employee identifiers, is a strong indicator of a ghost vendor. Employees who refuse to take vacations or resist new financial controls may also be protecting an ongoing scheme.

Monitor payment patterns for anomalies

We run regular reports filtering for duplicate invoice numbers, repeated payment amounts to the same vendor on different dates, and sudden spend spikes with a single vendor. If a vendor that usually invoices a steady amount suddenly bills far more without a clear reason, that change should trigger review. Vendor complaints about non-payment when your records show the payment was made are often the first clue of payment diversion.

How to prevent vendor fraud

Most growth-stage teams don't need enterprise software to prevent vendor fraud. A short list of procedural controls that create real checkpoints works, even when one person is wearing five hats.

Build a verified vendor onboarding process

We recommend making W-9 collection a hard requirement before any first payment (start with the IRS Form W-9). If you're in the "AP lives in email" stage, this one step alone cuts the number of vendors that get paid without any identity trail. It costs nothing to implement and creates a baseline record for every vendor in the system.

Once you have the W-9, a short checklist covers the rest of what matters for your procurement process:

• Legal name and Tax ID verification: Confirm through the IRS TIN Matching program that the vendor's name and EIN actually match, which catches shell companies using fabricated identifiers.
• Business registration check: Look up the vendor through the relevant state Secretary of State database to confirm the entity is active and in good standing.
• Exclusion and sanctions screening: Run the vendor through SAM exclusions and an OFAC search to flag debarred or sanctioned entities before you send a first payment.
• Employee cross-check: Compare the vendor's address and Tax ID against employee records, since overlap between the two is one of the strongest indicators of a ghost vendor scheme.

These steps add 15 to 20 minutes per new vendor, but they close the gap that most ghost vendor schemes exploit.

Enforce segregation of duties in AP

No single person should control a transaction end to end, from vendor setup through payment. If you're too small for full separation, the owner or COO reviews all new vendor additions, banking detail changes, and higher-dollar payments. Independent bank reconciliation matters here too: if the person who can change vendor bank details is also reconciling the bank, the "control" is mostly theater.

Use three-way matching on every invoice

Before paying an invoice, match it against the purchase order, the receiving document, and the invoice itself. Without a matching PO and receiving confirmation, the invoice shouldn't get paid. Even a manual checklist closes this gap if you don't have ERP software (see our overview of three-way matching).

Run regular vendor master file audits

We review the vendor file on a set cadence for anomalies that point to fraud risk. Even a well-maintained file drifts over time as employees leave, vendors merge, and banking details change. Quarterly reviews catch most issues before they compound.

Each audit should flag these four categories of anomalies:

• Duplicate vendor names or Tax IDs: Multiple entries for the same entity create openings for duplicate payments that slip through normal processing.
• Employee address matches: Any vendor whose address overlaps with an employee's home address warrants immediate investigation.
• Inactive vendors with recent changes: Vendors dormant for 12 or more months that suddenly show banking updates are a strong signal of impersonation.
• Recent banking detail changes: Any routing change in the last 90 days should be verified directly with the vendor through a known contact, not the details in the change request.

Anything that looks off during the audit should be documented and escalated before the next payment run.

Train employees to spot and report fraud

Employee tips are often the fastest way fraud gets surfaced, especially where formal controls are light. If you want people to speak up, they need to feel safe doing it. That means an anonymous reporting channel, a documented non-retaliation policy, and regular training that walks through common schemes in plain language.

What to do if vendor fraud is discovered

What happens in the first 48 hours determines whether evidence gets preserved or accidentally destroyed. We've seen companies lose recovery options because someone "cleaned up" records before legal got involved. These four steps should happen immediately:

• Preserve all records: Don't destroy any documents, even ones that seem unrelated. Collect all invoices, contracts, emails, and payment records, and lock down system access logs.
• Restrict access and call legal counsel: If you suspect an internal actor, revoke their system access carefully and talk to legal before taking action against individuals.
• Engage a forensic accountant: Bring in a specialist to trace losses and identify where controls failed. If tax violations may be involved, counsel can advise on filing IRS Form 3949-A.
• Review insurance coverage: Check whether your policy covers employee dishonesty, fraud, or social engineering, and notify the carrier as early as counsel advises.

Whatever the investigation uncovers, use it to tighten the controls that let the scheme happen in the first place.

How to close the most common vendor fraud gaps

Vendor fraud in most small and mid-size businesses comes down to a few elementary control gaps: no vendor verification, no independent reconciliation, and one person controlling the payment process end to end. Closing those gaps doesn't take a big budget. It takes clear ownership of a short list of controls.

We recommend starting with the four controls that close the most common gaps:

• Segregation of duties: Keep vendor setup, invoice approval, and payment execution with different people, or use owner-level review as a compensating control.
• Independent bank reconciliation: Make sure the person reconciling the bank isn't the same person who can change vendor payment details.
• Verified vendor onboarding: Require W-9 collection, TIN verification, and employee cross-checks before any first payment goes out.
• Anonymous tip reporting: Set up a channel where employees can report suspicious activity without fear of retaliation.

AP automation tools like Ramp can add duplicate detection, approval workflows, and better audit trails on top of these basics. But automation reduces certain risks without eliminating fraud. We'd start with the controls above, then layer in technology where it meaningfully tightens things up.

Frequently asked questions about vendor fraud

What is the most common type of vendor fraud?

Ghost vendor schemes are among the most frequently reported. An employee creates a fake company in the payment system and submits invoices that route payment to themselves. Duplicate invoicing and overbilling are also common, especially because they hide within legitimate vendor relationships.

How do I verify if a vendor is legitimate?

Collect a W-9 before any first payment, verify the legal name and Tax ID through the IRS TIN Matching program, confirm business registration through the state Secretary of State database, and cross-check the address against employee records. A simple onboarding checklist plus a second-person review catches most of what matters.

Can AP automation prevent vendor fraud?

It can close several gaps but won't eliminate fraud on its own. Automation tools flag duplicates, enforce approval workflows, and create stronger audit trails. If the same person can still create a vendor, approve the invoice, and send the payment, software won't save the process.