Earlier quoted context omitted.
What was the fee putatively for? Was it a cleaning fee that would have been less per day on a longer rental? It doesn't seem right to call something a "service fee" if it doubles the total purchase price.
Engaging at any level with the idea that the fee is for any purpose other than lying about price in advertisements is giving it too much credit.
But fees are many times also used to avoid or evade taxes and royalties. For example, resort fees can be used by hotels to avoid paying royalties to the franchisor.
There is never any good excuse to hide or gatekeep the total price from a customer though.