> "Amazon UK" is actually Amazon Luxembourg. Visa wasn't picking on them, they were applying the standard cross-border tariff.

Actually if we're nitpicking its a UK branch of Amazon Luxumbourg (UK Company No. FC032354 UK VAT Number: GB 727255821).

But that's not really the point. The crux of the matter was not Amazon, but it was UK-issued VISA cards accepted on Amazon UK (and the post-Brexit removal of the EU’s European Interchange Fee Regulation cap).

Which basically brings us back to the cross-border topic at hand (i.e. EU or branch-of-EU company accepting UK cards).