Remember, they also charge the selling company a percentage of the sale, which is added into to the price of the item - so you still wind up paying them to use the card - just a smaller amount.
Well, in the sense that I also am paying a small amount for the merchant's lights, heat, taxes, employees, etc., yes. All that IS factored into the price of the item being bought... all "overhead" is. There's no way to avoid that. But, as far as a DIRECT additional charge for using the card - no, there is no actual add-on charge (unless you're talkin' gas stations for instance). In that same sense, CASH CUSTOMERS are paying for that same credit card overhead as well.
And that's another thing I don't 'get'. A merchant will pay a credit card company "X" % on each transaction charged to a 'card...but won't give his customer a discount for cash! Go 'figger'!