Anyone has an oz of brain, should know you never argue with officials / border control / custom officers... This is the same everywhere, incl in USA. You do not want to give them any excuse to make your life difficult!
All our 3 trips to South Africa used JNB as entry / exit point. We did not encounter any issue. In fact on the first trip I went to ask police where to find the ATMs. The 2 guys took me to the domestic side where there were several ATMs by the bank offices. The international side is separated from the domestic side with a rotondo type big hall. All the shops and restaurants, incl 2 mini supermarkets, are on the domestic side.
