Credit card fees
Did you ever wonder how much merchants are charged when you use your credit card? The website True Cost of Credit provides you with these numbers for major credit card providers – the numbers are for the US though. Given that the fees are not insignificant (somewhere between 2-4% in most cases and can go as high as 18% for e.g. gums) one could easily imagine that these fees eat up a lot of the profit margin or in turn are at least partially passed on to the customer.