We now a days prefer to pay by cards when we dine out. Paying by cards is more convenient. No hassles of carrying cash, waiting for the change and so on.
The standard process is to handover your card to the waiter who goes to swipe it. There are wireless terminals available, some people have experienced the waiter directly asking for PIN. Never ever share it publicly.
The waiter will first swipe your card on his gadget that stores the data from the magnetic strip of your card and then actually swipe it at the official terminal. There are cameras watching you punch in the PIN of your card as well as the people at the counter. Make sure no one is actually watching you. What you can do is cover the keypad with your left hand and punch the PIN with the right hand. Easy?
The waiter can clone your card exactly and use it to either shop online or withdraw cash from ATMs. These guys would be really difficult to trace as well. Use your cards wisely. Make sure they are always in your custody.