There is a small charge charge collected by the credit card company on all Mastercard/VISA/Amex/Diners Club transactions irrespective of whether the cardholder is using a debit/credit/pre-paid/no commission cards.
So for example, if you pay €1, the merchant will received something like 99.5 cents with the payment scheme collecting 0.5 cents before it settles with the merchant. This is called the 'Interchange' and is subject to ongoing monitoring by worldwide regulators to ensure the card payments schemes do not abuse their market dominance.
The small fee is in effect the cost the the card issuing comapnies and the merchants have to pay to maintain the payment scheme infracstructure.
The attached Mastercard link provides more details and it shows that in certain situations the prepaid card is more expensive for the merchant to process than a normal credit card. So although a good dea, on the face of it, for the holiday maker , not so good for the local SS businessman which this forum so loves to support!!
http://www.mastercard.com/us/company/en/whatwedo/interchange/Intra-EEA.htmlAn interesting topic and one which paid me well for 8 years :-)