So if you buy a $2 Coke, it's not a $0.054 fee (2.7%), it's $0.354 (or a whopping 17.7%).
Maybe my dentist evades a few taxes, I dunno. But people buy cheap things at the bodega, so it probably is closer to the actual fees.
If it says debit on the front of the card, it is debit.
I’ve never seen this work in person, but some people claim their debit card worked as a credit card and whatnot. Even if that is true, all merchant systems I’ve worked with allow the merchant/cardholder to select debit or restrict transactions to only debit.
This isn't the full picture. Debit card transactions might only be a few cents. But you still have to pay a fixed cost for the machine and related bits. For some businesses, that cost might be too high to justify.