Yea, taken to the extreme, I don't think anyone would think it's fair:

Restaurant A's pasta is $14.95, printed clearly on the menu.

Restaurant B's pasta is $13, with a 15% service fee written in tiny letters on the menu somewhere.

Restaurant C's pasta is $2.99, with a 500% service fee written in tiny letters on the menu somewhere.

You're paying the same thing at each restaurant. If you think C is sneaky and unethical (which I hope everyone would), then why is B ok?