I have camped twice with 2 vehicles, and have not been charged extra once. We have always made sure that we have made the gate and the camps we have checked in at aware that we have 2 vehicles, and have always been given 2 exit permits.
How is it possible that 2 cars can be on one site if no extra charge was payed. Surely each vehicle needs an exit permit and the same reservation number cannot be used for more than one vehicle so that the park can control the vehicles coming in and out. The only way to get around is to ask for two separate exit permits at reception and thereby having it on record on the system . The reservation system should then automatically pick it up as two vehicle pet site and charged for the extra vehicle.
If it does not work that way what control is there then for more than 1 vehicle to use the same reservation number and only pay for one site instead of two. Currently there is no control at the camp sites and any one can enter, pitch a tent / park a caravan without any one checking if the booking is for the correct number of vehicles / caravans / persons. The current rate is from R190 for 1-2 persons plus R60 for each extra person. A total of 6 people thus pay R430 per site for one power point. This can be quite a loss in revenue if it is so easy just to pitch up and camp with friends.
When you fill in your gate form you have to state how many people in your car and that is on the permit, if it is different to the number of people in the car you wont be allowed entry, also surely when checking in for camping that number is also checked?
Or is it sadly people just not taking the extra effort to do something, I recently took 2 German friends to KNP. Myself and my Father both have wild cards, but after check in I had to ask why there had been no conservation fee's charged for my friends and I got the reply "but you have a wild card". I dont think enough care is taken when people check-in at gates or at camps.