That sixteen digit number that is printed across the middle of your credit card is the key to a potentially big credit limit. You know what your own credit limit is and you don't buy more than you can afford. But supposing a fraudster got hold of your credit card? What would happen then?
The answer is that they would try and spend as much as possible on it before they got caught or the card was stopped. This is why you need to guard against anyone finding out anything about your credit card. You need to make sure you don't share the sixteen digit credit card number with anyone, regardless of who they might be. You just never know when someone is looking or has an unhealthy interest in your card details.
You shouldn't just assume that all cashpoints and other points of contact for a credit card are innocent either. Always check for anything untoward and make sure you protect your card as much as possible.
Of course you wouldn't let your card go out of your sight in any circumstances. Nowadays there are chip and pin machines so there is no reason why anyone should even touch your card. You slot it into the machine when prompted, enter your pin number and remove it when the payment has been made. No shop assistant should have the need to touch it or even look at it at all.
Always shield your card and make sure no one sees you entering your pin number either. Don't be modest about doing this - it is your private information and no one else should know what it is. If you feel someone is too close take the terminal and move out of their way. The chances are they will feel embarrassed anyway!
In short it is up to you to make sure you keep your card secure at all times. Even then you can never be 100% safe, but it will certainly make a difference. Check your statements regularly too, and if you see anything you don't recognise make sure you bring it up and check it.