Exactly. They have already built it into their prices. You are paying the CC fee when you buy anything. IF you ask for a cash discount then they can knock off the CC fee or something and sell it to you for less for cash. In some places, Texas is one, it's illegal to charge extra for CC's but merchants can 'discount for cash'. Sometimes they advertise it and most of the times they do not except for fuel where a lot of stations show the credit price and the cash price on the sign. (But if they said +.10 for credit, it would be illegal)
Then you have Walmart where they give you a .10 discount if you are a + member and you can use any CC. Costco has a 'lower than most' gas price and you get CC 'points' on their CC when you pay with that.
I've gotten some good deals in stores by asking for the 'cash discount'. If they don't want to discount I'll just pay with a CC and get the cash rebate from the CC.
But even then I know the overall prices still include a cushion because of CC fees.