VAT Validation for Multi-Vendor Marketplaces: Who Checks Whom

A marketplace has at least three parties in every transaction – the platform, the vendor, and the buyer – and VAT validation applies differently to each. The short answer to ‘who checks whom’: the platform validates the vendor’s VAT number before onboarding them as a business seller, and separately validates the buyer’s VAT number when a transaction’s tax treatment depends on the buyer being VAT-registered (typically B2B). Same lookup, same underlying source, two different reasons to run it.

The rest covers both sides, where deemed-supplier rules fit without turning this into a tax memo, and how to run the checks at marketplace scale rather than one vendor at a time.

Validating Vendors at Onboarding

Before you list a business as a seller, you want to know their VAT number is real. That means running it through VIES – the EU’s VAT number lookup – and checking two separate things that people conflate:

• Format validity – does the string match the country’s checksum pattern? This catches typos instantly and needs no network call.
• VIES registration status – is that number actually registered in the issuing member state’s system right now? A number can pass format validation and still not be registered – format is a syntax check, not proof of registration.

A VIES check is evidence a VAT number was registered at the time of the query – not a certification of the vendor’s business or a guarantee it stays valid. It doesn’t tell you the vendor is solvent, trustworthy, or who they claim to be. It tells you a specific VAT number was on the books in a specific country’s system at a specific moment. Treat it as one input to onboarding, not the whole decision.

Company name and address detail in the response varies by country – some national databases return a full trader name and address alongside the valid/invalid flag, others return only the flag. Don’t build a vendor-matching workflow that assumes every country hands back a name to compare against your KYB records; for enriching a VAT number with company data beyond what VIES itself returns, you may need a country-specific source on top.

Two prefixes worth getting right before they cost you a support ticket: Greece uses EL, not GR, and Northern Ireland uses XI – goods only, since VIES doesn’t cover Northern Ireland services.

Validating Business Buyers

The other side of the same endpoint: when a buyer claims to be a VAT-registered business and the transaction’s treatment depends on that, you check their number too. What that treatment actually is depends on what’s being sold.

For cross-border B2B services, the customer typically self-accounts for VAT under reverse charge (Article 44 place-of-supply, Article 196) when the seller isn’t established in the buyer’s country. For cross-border B2B goods, the mechanism is legally different even though people also call it ‘reverse charge’ colloquially – it’s an exempt intra-Community supply on the seller’s side (Article 138) paired with the buyer’s intra-Community acquisition (Articles 2(1)(b) and 20). The two aren’t interchangeable, and a marketplace selling both goods and services shouldn’t blur them into one workflow.

Either way, the buyer’s VAT number being valid is necessary but not sufficient. The transaction facts – what’s sold, to whom, under what terms – have to actually support the treatment. Validation alone never proves eligibility for reverse charge or zero-rating; it’s one condition among several. For a fuller breakdown of when a check is actually load-bearing for a transaction, see when to validate a VAT number.

Deemed Supplier: Where the Platform Itself Gets Pulled In

There’s a separate wrinkle specific to marketplaces, worth naming even though it’s outside VAT number validation itself. In some fact patterns, EU VAT law shifts VAT liability onto the platform – the ‘deemed supplier’ rules under Article 14a of the VAT Directive. They apply to specific scenarios: certain imported low-value goods, and goods sold within the EU by a non-EU-established seller through an electronic interface. It’s goods, not services, and the scope isn’t static – the rules have evolved and may again.

This is not tax advice – whether deemed-supplier rules apply to your marketplace depends on your specific goods, seller locations, and transaction flow. Talk to a tax adviser before relying on this for compliance decisions. Vendor VAT validation and deemed-supplier liability are two different questions; solving the first doesn’t answer the second.

Audit Evidence, at Marketplace Scale

A marketplace doesn’t run one VAT check – it runs one per vendor onboarded and, depending on volume, one per qualifying transaction. When an auditor asks you to justify why a vendor was treated as a valid business seller, or why reverse charge was applied to a specific buyer, ‘we looked at VIES once’ isn’t a record – a stored, timestamped result is.

VIES can return a VIES consultation number on a requester-qualified lookup: a timestamped reference showing a specific check happened at a specific moment. Some tax authorities (French and German practice, notably) look for it on audit. It is not a tax certification and it doesn’t adjudicate any specific transaction – it’s contemporaneous proof the lookup occurred, nothing more. It’s also not unique to any one provider; several VAT APIs return it. What actually differs between providers is how much friction it takes to get one on every check.

On vatnode, that friction is one-time: set your requester VAT once in dashboard Account details, and every vendor or buyer check – single or bulk – automatically gets a consultation number when VIES issues one, with no per-call parameter to wire into your integration. A requester-authenticated call uses VIES directly rather than falling back to a national source, because the consultation number is VIES-specific evidence; a national registry can’t produce it.

Every response also carries a source field – VIES, CACHE, or a national code – so you always know which system actually answered, and a consultationNumber field that’s always present as a key even when its value is null because VIES didn’t issue one for that check. That’s the accurate version of ‘never-null’: the field is always there for your code to read, not that every check magically succeeds.

Ongoing Monitoring Across Many Vendors

A VAT number valid at onboarding can lapse or deregister at any point after. That’s true for a single supplier relationship, but a marketplace with hundreds of vendors has hundreds of independent places where it can happen without anyone noticing – no vendor is going to volunteer that their VAT registration was cancelled.

There’s no legally mandated re-check interval; this is operational risk management, not a compliance clock. The practical pattern is to validate at onboarding and then monitor vendor VAT IDs on a schedule that matches your exposure, rather than treating the onboarding check as permanent proof. VAT monitoring that pushes a webhook when a previously-valid number goes invalid means you find out when it happens instead of during your next audit.

Doing This in Code

The endpoint is the same for a vendor onboarding check and a buyer check:

curl https://api.vatnode.dev/v1/vat/DE123456789 \
  -H "Authorization: Bearer $VATNODE_API_KEY"

The response includes valid, vatId, countryCode, countryName, companyName, companyAddress, checkId, verifiedAt, source, and consultationNumber. If the call fails upstream, you get a typed error instead – VIES_UNAVAILABLE (503), VIES_ERROR (502), UPSTREAM_TIMEOUT (504), RATE_LIMITED (429), or INVALID_FORMAT (400) if the string never had a shot at being a real VAT number. A marketplace onboarding flow should treat those as ‘try again’ states, not silently reject a vendor because VIES had a bad moment.

A vendor roster or a buyer list at any real marketplace volume is a bulk VAT validation workload, not a loop of single calls – submit the whole roster as one job and poll it. The job paces its own concurrency against VIES, so you’re not the one deciding how hard to hit the endpoint. Vendors and buyers also span a lot of countries fast for any marketplace with real reach; check country-by-country coverage for where national fallback applies. For a subset of member states, if VIES itself is temporarily down, vatnode falls back to that country’s own tax authority or company-registry API so you still get an answer – except on a requester-authenticated call, where fallback is disabled because the consultation number is VIES-only evidence.

If your marketplace is itself a SaaS platform selling to EU business buyers, EU VAT for B2B SaaS covers your own reverse-charge obligations separately from what you check on your vendors. And if you’re weighing whether to query VIES directly instead of through an API, a production VIES alternative covers what ‘just call VIES’ leaves out once you’re doing it for hundreds of vendors instead of one.

Coverage spans the EU-27 plus XI for goods, including German VAT numbers, French VAT numbers, and Dutch VAT numbers.

This is general information about EU VAT and VIES, not tax advice. Whether reverse charge, deemed-supplier rules, or any specific tax treatment applies to your marketplace depends on facts we can’t assess here – confirm your own obligations with a qualified tax adviser.

FAQ

Does a marketplace have to validate seller VAT numbers?

VIES itself doesn’t mandate anyone check anything – it’s a lookup service, not a legal requirement. But validating a business vendor’s VAT number is the standard due-diligence step before onboarding them or applying reverse charge to their transactions, and it’s what an auditor will expect to see. This isn’t legal advice – confirm your own obligations with a tax adviser.

How often should a platform re-check vendor VAT IDs?

At onboarding, at minimum. A number valid at signup can lapse or be deregistered later, and a marketplace with hundreds of vendors has hundreds of independent points where that can happen unnoticed. There’s no legally fixed re-check interval – treat periodic re-validation as operational risk management, not a compliance deadline, and consider monitoring vendor VAT IDs on an ongoing basis rather than only at onboarding.

Does vatnode validate both vendors and buyers on a marketplace?

Yes – the same GET /v1/vat/:vatId endpoint checks any EU VAT number, vendor or buyer. vatnode doesn’t distinguish between roles; the marketplace decides which party’s number it’s checking for a given transaction and calls the endpoint accordingly.

What about deemed-supplier VAT rules for marketplaces?

In some fact patterns, EU VAT law shifts VAT liability onto the platform itself – the ‘deemed supplier’ rules under Article 14a of the VAT Directive. Whether they apply depends on your specific goods, seller locations, and transaction flow, and the rules only cover certain scenarios (not every marketplace transaction). This isn’t tax advice; talk to a tax adviser before relying on this for compliance decisions.