> In fact, if you come across a merchant that accepts credit with a minimum purchase amount or tacks an extra fee, you can take the receipt and call the terminal owner (visa/MasterCard) and report it. The receipt has a terminal ID, and it turns out the likes of Visa get really pissed if merchants do that.

This also varies by country, but I think Visa/Mastercard relented on it in many jurisdictions.

In Australia, for example, merchants have been allowed to add on credit card fees everywhere, and their card readers automatically tack on the fee when they detect a credit card.