Please know your facts before making such statements.
Having worked for Woolworths recently in a management capacity I can assure you there is a minimum spend on credit cards (Amex & Diners specifically).
We are not talking about EFTPOS or Credit Cards in general, we are discussing Amex cards, hence my statement
I have also used it many times for under $5 in Coles, Woolworths and even IGA...
If there is a minimum.... management should tell their staff to enforce.. or have the system do it for them (you would their system would be complex enough to manage that)... cause they don't enforce it with me.