Plain language and clear notification is necessary. Just "included in the terms" is not enough.
But and body can ask anybody for almost anything and if it is provided then no illegality.
Send money now: Acc: 1927-3938277-00
You all owe me US$100 for reading this. Pay now!
I have no intent to purchase anything from you, unlike the customers (i.e. people who have and continue to purchase) who this thread is discussing.
An actual analogy would be more like "You all owe me $100 for reading this, if you want to purchase something else from me". Which is completely legal. In any jurisdiction. If you don't like it you're free to go buy from someone else.