you just display the price with your local VAT. In the last step, if the user is from a different country AND if you do more than 100k eur revenue for that country/year, you recalculate with the correct user VAT.
And if you are Amazon, you then give the diff as a discount if it was more than advertised.
And if you are Amazon, you then give the diff as a discount if it was more than advertised.