I just got back from several days in SA, renting in Jo'burg and driving around Pretoria then to Kruger NP and around there.

I rented from Avis (booked via Rentalcars.com), got the Mercedes C-Class I booked (had a choice of a CLA instead, but the C-Class was better equipped). It was this year's model with only 7000 km on it and no faults except a very small dent. The staff were helpful and efficient when picking up, and had no problem giving me an extra day's rental when I realised I had messed up the reservation and made it from the day after I arrived. On return they were also efficient and very friendly, and did not take exception to the car being absolutely covered in dust (or battered underneath by occasional rocks and deep potholes in dirt roads). I would rent from them again.

I had a GPS with SA maps, borrowed from a work colleague, but didn't use it. I got a prepaid data SIM from the Vodacom store in the airport and used Google Maps on an iPad to navigate and this worked fine. The only places without good mobile coverage were in the Kruger NP (which has a simple enough road network that their paper map is sufficient) and a couple of spots on main roads west of Hoedspruit in deep valleys, which didn't cause a problem. Between the good mobile coverage and some offline maps from Open Streetmap (I use the "OSMAnd" app on my phone) for backup, as well as paper overview maps from the car rental agency, I had more than enough mapping available. SA also has fairly good signage on the roads. I definitely would not pay for a GPS unit with the car.

I avoided traffic stops, mainly by slowing down to obey the speed limit when it dropped suddenly 120-80-60km/h just before a bend in the road - and a couple of times there were police pulling people over just past the bend. It's an obvious place to set a speed trap. Other than that I just kept within 10-20km/h of the speed limit, which isn't hard - the speed limits outside towns are pretty high. So fines didn't come into question, but I was advised by a tour guide I met at the safari lodge we stayed at that if I was asked to pay immediately I should politely suggest we go to the police station so I could do so (if I had time, obviously if close to a flight deadline, I might have to pay up ). He stressed that I should always avoid handing over cash if possible, since I might get fined anyway and would have to pay again later. This all seemed quite logical to me.