I looked this up just now and apparently Amazons case is more complicated due to things like sold by Amazon (16%) vs third party sellers (they got to choose if they pass it down to the customer or not). It was an economy stimulus after all.

And apparently fixed book prices (printed on the back) were up to every single publisher to decide about

Then you also have different VAT rules depending on the product category. Food is 7% in Germany.

Lastly I also remember that Amazon gift cards were weird for a few hours. Something like you pay 48.50 and got 50€ worth of credit. I can’t remember if you could then use that credit to buy new gift cards.

Lots of ways where this becomes quite a complex problem real fast