Charging more than you say is not a 'hidden fee' it is fraud. Hiding the fee in the total price is exactly a 'hidden fee'.
To this point, look at @exogen's extremely helpful demo of the service he posted. Can you tell how much the fee was? I was curious, so I actually went to Octo Sushi's site and tried to mock up a fake similar order, and I couldn't figure out if there even was a fee added on top of Octo's price or not.