Taking the tip credit of 2.13 per hour is a privledge afforded to restauranteurs under the circumstances that they track your wages and pay you wnenever you do not make the federal/state minimum wage. THEY pay you 2.13 per hour and the customer pays you the rest. If you do not get it from the customer, you have to fill out a form and your employer has to pay you the difference.
I know of no obligation to tell anyone you are a tipped employee. As long as you gross the federal minimum wage, your employer owes you nothing further.
You are taxed on your 2.13 per hour, and you are also taxed on the tips you report, or a statutory minimum. If you say you received 6 an hour in tips, they take taxes on that amount, but they don't take the entire amount. Just the taxes. It is a fair system. However it often does not work in buffet restaurants because people think you are not a tipped employee. You'd be better off to go work in a diner than work in a buffet restaurant when it comes to tips..