Be selective with the truth on your customs form...
It's a well-known fact that Nigeria is very much a cash economy, so most Nigerian visitors will carry large amounts of cash. The question is, how can you know for sure what a person has on him, his nationality and the address he's heading to? Easy, use his customs declaration form, aka robbery-application! Every passenger has to fill one in, and it contains the address you're heading to, items being imported and even the amounts of cash and currencies in your posession. You have customs officials colluding with criminals outside. And no, I don't have proof, the proof is in the numbers of victims and m.o., and it's not just Nigerians having trouble! Best bet is to avoid JNB at all costs, or travel in large groups. Crime and corruption is a national sport in South Africa, and don't expect much help from the police either. As long as you are aware of these issues you will enjoy your time there, well, usually...