A better argument is that advertising that a product is available to "buy now", but changing the terms at checkout to "buy a license" is a type of fraud known a

A better argument is that advertising that a product is available to "buy now", but changing the terms at checkout to "buy a license" is a type of fraud known as "bait and switch". An offer is being made that the seller has no intention of honoring, with a different product (the license) offered as a substitute.