I think what go is saying is that credit card companies have trained us to spend more money by using credit cards. It is possible that you are in a small minority of people who has common sense™ but most of us (including me) tend to spend more or simply decide to spend or not bad on the small stimulus. Again, I'm not accusing you of irresponsibility. I'm just saying what I think is common.

Edit: I agree. If you're making an expense anyway, it is obviously better to get the highest reward you can get. But we're talking local optimization now.

I'd ask for a cash/direct debit discount instead. Cut out the middleman.

As an operator of multiple businesses, I much prefer customers who pay with cards than cash. There is a high cost to handling cash, making sure employees don't steal, counting it, getting change from bank, depositing it, etc. Therefore, it might not behoove the owner of the business to provide a cash discount.

Direct debit (or cash). Rental is more often done with direct debit than credit cards.

It would be nice to offer a discount for debit cards, but unfortunately, the card processing systems I've seen don't have the capability to determine credit vs debit and charge different price for it. It would be great if merchants could automatically charge people with rewards credit cards more.