If you consider selling to professionnal that are not in your country, you have to ask for a number that only professionnal people can have.

On the begining of my shop, my VAT number module was not required for professionnal because there are some professionnal (association etc... that couldn't provide this number).

The problem is that some individuals customers registered as professionnal and didn't fill their VAT number to be invoiced without VAT.

So about VAT number, I thing there is 3 things to do to avoid this kind of abuse :

• If the role of the user is professionnal, make the society field required for billing address
• Next to the VAT field (see my screenshot above), provide a checkbox "I dont have a VAT number", if checked, the VAT number field is changed to another required field, that all society in the world could have (I believe this society number exist)... Something that could certify that the society name filled in the billing address isn't a fake
• Make verifications as much as possible. Verify if the VAT number is correct with the SOAP service in case of the user choose to fill the VAT and verify that the society number is correct via another SOAP service (if one exist) with the society number