A vendor onboarding checklist is a short list of documents and checks to finish before you pay a new supplier. The core items are a signed tax form, a verified tax ID, a confirmed business identity, a signed contract and bank details checked by phone. Doing them in order prevents wrong payments, missing paperwork and fraud.
This guide gives the list in eight steps. It then explains the tax forms in plain terms and shows how to scale the review to the risk.
The vendor onboarding checklist in 8 steps
- Confirm the need and the approver. A named person in the buying team signs off that the purchase is approved and funded.
- Collect a signed tax form. A US vendor sends Form W-9. A non-US individual sends Form W-8BEN. Details are below.
- Check the tax ID. Compare the name and number on the form with the contract and the invoice.
- Verify the legal entity. Confirm the business name, address and contact with a second source, such as a state business registry.
- Get the contract in place. Payment terms, scope and prices should be signed before work starts.
- Confirm the bank details by phone. Call a number you already trust, not one printed on a new email.
- Run a risk check. Match the depth of the check to what the vendor will touch, such as your data or your customers.
- Set up the vendor record. Enter the verified details once, restrict who can edit them, and keep the paperwork on file.
Finish every step before the first invoice is approved. A missing form found later is slow and awkward to fix, because the money has often already moved.
Sources: Internal Revenue Service, About Form W-9 and About Form W-8BEN (irs.gov)
Collect the right tax form
Ask for the tax form on day one. It is the one document the tax authority expects you to hold for many vendors.
US persons use Form W-9. On it, the vendor lists its legal name and its business type, and gives its taxpayer identification number (TIN). The vendor then signs under penalties of perjury. The IRS lets you use your own "substitute" W-9 if it carries the same certifications.
Form W-8BEN is for a foreign individual who is the beneficial owner of US-source income. The IRS instructions say the form should reach the payer before the money is paid or credited. A foreign business entity uses a different form, W-8BEN-E.
The IRS says that if a requested W-8BEN is not provided, the payer may have to withhold tax at 30%. The cost of skipping this step is real.
Sources: Internal Revenue Service, Instructions for the Requester of Form W-9; Instructions for Form W-8BEN (irs.gov)
Check the tax ID before you rely on it
A form with the wrong name or number causes trouble at year end. The IRS treats a payee who gives no TIN, or a TIN that does not match, as a possible case for backup withholding. The backup withholding rate is 24%.
Start with a simple desk check. Does the legal name match the contract? Is the form signed and dated? Does the business type fit what the vendor sells?
The IRS also runs a TIN Matching program. It lets approved payers check name and TIN pairs against IRS records before they file information returns. Not every company can use it. A payer must apply through IRS e-Services and be listed in the IRS Payer Account File database. If your company cannot use the program, the desk check and a careful look at the signed form are still worth doing.
Tell your tax advisor how you plan to handle mismatches. This guide is general information, not tax advice.
Sources: Internal Revenue Service, TIN Matching (irs.gov); Instructions for the Requester of Form W-9 (irs.gov)
Verify who the vendor really is
Tax forms prove what a vendor says about itself. They do not prove it is real. Add a second source.
- Business registry. Most US states publish a searchable list of registered companies. Match the legal name and status.
- Address and phone. Confirm both through a channel you chose, not one the vendor supplied in the same email.
- Contact roles. Record who signs contracts, who answers billing questions, and who can change bank details. Keep them as separate roles.
- Insurance and licenses. If the work needs a license or coverage, ask for the certificate and note its end date.
Keep copies of what you checked. A short note with the date and the name of the person who checked is enough.
Sources: Internal Revenue Service, Instructions for the Requester of Form W-9 (irs.gov)
Lock down bank details and payment terms
Changed bank details are a common route for payment fraud. Treat every new account number and every change as a risk event.
- Call back on a phone number from your own records or the signed contract.
- Ask for a bank letter or a voided check, and compare the account name with the legal name.
- Have another staff member sign off before any bank detail is changed.
- Write the payment terms into the vendor record, such as net 30, so invoices are paid on the agreed day and no sooner.
A small, repeatable call-back step is cheap and catches many fake requests.
Sources: none cited; this section is practical advice from the editors, not a regulation.
Match the depth of review to the risk
Not every vendor needs the same review. A one-time office supply order is low risk. A vendor that stores customer data or runs a core system is not.
| Vendor type | Suggested extra checks |
|---|---|
| Low risk, small spend | Tax form, registry check, bank call-back |
| Medium risk, ongoing service | Add a signed contract, insurance certificate and a named account manager |
| High risk, touches data or operations | Add a security questionnaire, a review of independent audit reports, and a backup plan if the vendor fails |
Write the tiers down once. Then each new vendor lands in a tier by a simple rule, and no one has to guess.
Sources: none cited; the tiers are an example from the editors, not a rule.
Sources
- Internal Revenue Service, "About Form W-9, Request for Taxpayer Identification Number and Certification." irs.gov/forms-pubs/about-form-w-9
- Internal Revenue Service, "About Form W-8 BEN." irs.gov/forms-pubs/about-form-w-8-ben
- Internal Revenue Service, "Instructions for the Requester of Form W-9." irs.gov/pub/irs-pdf/iw9.pdf
- Internal Revenue Service, "Instructions for Form W-8BEN." irs.gov/pub/irs-pdf/iw8ben.pdf
- Internal Revenue Service, "Taxpayer Identification Number (TIN) Matching." irs.gov/tax-professionals/taxpayer-identification-number-tin-matching