Usually, applied in small value purchases (>100$) with POS Credit Card payments is raising on popularity.
If you are asked to enter your PIN twice, be sure to also check twice if you are paying the amount of your PIN :)
Chargeback? Unlikely, since you authorized the transaction, probably without even keeping a copy of your bill. If additionally asked to sign, be sure to double check you are not paying the amount of your PIN :)
Pay attention on some devices that prompt for a gratuity to be entered. In UK and most of Europe, this is likely a way to go.