A VAT number tells you a company exists. This tells you what it actually does — industry, legal form and status, straight from the free KVK Open Dataset.
VIES validates the number and returns the registered name. This one tells you what the company does — together they answer "is this a real business customer?" in one go.
It reads the KVK Open Dataset Basis Bedrijfsgegevens, which is public. Nothing to sign up for, nothing to pay per lookup.
Looking a company up changes nothing in your store. Any follow-up action — moving a customer to another group, say — is Mago Core's job, and still needs your OK.
Requires Mago Core. The KVK Open Dataset is public, so there is no key to configure.
composer require mago-assistant/magento2-kvkbin/magento module:enable MagoAssistant_Kvk && bin/magento setup:upgrade