you dont quarrel with officials, even in the good ole US!

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.