Stephen Sprunk writes:

Really?

I deal with several merchants that have self-swipe terminals, and the
terminals ask _me_ if the card is debit or credit. If I press the
"credit" button, even when using my debit card, they do not ask for a
PIN or offer cash back. I've never tried pressing the "debit" button
when using my credit card since I can't remember the PIN.

Note that all (US) debit cards I've seen have the word "DEBIT" on their
face; I don't know if that's required in other countries as well. If
the cashier swipes the card for you, they _may_ be using that
information (and some ask the customer for the card type) to decide
whether to offer cash back.
In the UK our cards are mostly chip and pin, the terminal being on the
counter close to the customer. I have never been asked what type of card
I have, they just know and the type is often displayed on the screen
along with amount.

The cashier rarely gets close enough to see the card.

Inside McDonalds they usually walk away to get your food leaving you to
either put you card in the machine and enter your pin, when they come
back the till tells them you have paid, or then you pay cash. At drive
throughs they hand you the terminal, which is on a long telephone type
lead.

Only supermarkets/convinience stores offer cashback, as it reduces the
amount of cash they need to, pay to, bank. This is only on debit cards,
probably all sorts of consumer credit rules about giving cash on a
credit card.

Amex Cards are treated as a credit card by retailers, due mostly to
what it costs them, even though they are, usually, charge cards.

Phil