I agree. Tips should be unknown to the employer. This can readily be done even with card transactions; staff usually swipe a card or enter a PIN anyway to use the POS system.

One of my biggest hesitations with tipping in places where it is unexpected, like a muffin shop in the OP, is whether the tip goes straight to the employee whose performance I tipped for, split among all staff indiscriminately, or more sinister straight to the employer.