Upvote:5
While there might be a 'tax', the bulk of that is the 'currency exchange fee'.
That is how the currency exchange business gets paid. The transaction was β¬150 cash + β¬30.xx markup. The markup possibly consisting of 1) the unfavorable exchange rate, 2) commission, 3) merchant fees for using a debit/credit card 4) local tax.
The agent may have said 'tax' because it's easier to express and understand than commission. Though it is possible they use the word 'tax' to make it appear mandatory while a commission is something optional or negotiable.
There is nothing unusual about what happened. To note, you will almost always get a better deal from a random ATM then a currency exchange desk.