I believe it's the actual marketplace, amazon. ebay, aliexpress that are required to apply the VAT at the point of sale thus collecting it on the sellers behalf, then I would assume the seller has to print the marketplaces VAT number and post it, I would hope its that simple.distant marketplaces (e.g. Aliexpress) will actually do this, and so for now marketplace sellers will probably have a heavy incentive to fake the VAT numbers.