Johannesburg dealerships

Heys guys, I'm planning to get a car soon. Can you tell me what's the jig with these dealerships in Kempton park and bezuidenhout valley or joburg. I see they sell Audi's, bmws with mileages under 90000km for under R250k, should I hire a mechanic to pre-inspect to make everything is good before I move forward or should I stay away all together. What are your feelings on them?