I avoid carrying cash and prefer the disciplined use of a credit card for all my purchases.
Back to my story, luckily I had cash to pay for my purchase, but I decided to do some investigating.
According to the Visa website:
Visa has certain regulations that all merchants that accept Visa cards must follow. One of those rules is that Visa merchants are not permitted to establish minimum transaction amounts, even on sale items. However, in some countries surcharging is legal and the local legislation will take precedence over Visa's regulations.
The remedy, according to the Visa website:
If you run into a problem with a merchant, please notify your Visa card-issuing bank. Visa member banks have access to the appropriate Visa rules and regulations as well as to the Notification of Customer Complaint forms which should be used by the bank to document and file merchant complaints.
Unfortunately, based on my experience, SA banks don't seem capable of dealing with this problem (or it is legal here). Either way, since Visa doesn't allow me to complain directly, I am at a dead end.
This sort of thing is typical of small shops who whine about being squeezed by big chain stores, but also try to screw their customers (and, I suspect, the taxman) at every opportunity. Many of these small timers have no concept of customer service, and deserve to be obliterated.
Update. Help from an expert: http://mymoney.iafrica.com/expert_advice/664706.htm . Too bad my bank, after shunting me from pillar to post, eventually told me merchants were allowed to set minimum purchases. SA banks prove as incompetent at ever.
Update 2. Another example of this from a branch of a franchise takeaway.