If you don't notice a card skimmer and your card data does get stolen, take heart. As long as you report the theft to your card issuer (for credit cards) or bank (where you have your account) as soon as possible, you will not be held liable for the lost amount and your money will be returned. Business customers, on the other hand, don't have the same legal protection and may have a harder time getting the money back.
Just remember: If something doesn't feel right about an ATM, don't use it.