In terms of the Estate Agency Affairs Act (112 of 1976), every estate agent and estate agency firm must obtain a Fidelity Fund Certificate (FFC) from the Estate Agency Affairs Board (EAAB). It's illegal to operate as an estate agent unless the EAAB has issued you with an FFC for the current calendar year. It's also illegal to claim commission if you didn't have a valid FFC at the time you rendered the services to the client.
This applies not only to agents who sell residential property, but also to letting agents, commercial and industrial property brokers, agricultural property agents, business brokers, and agents who "exhibit" properties which are for sale or to let (e.g. 'showhouse sitters').
You can check the validity of an agent's FFC on the EAAB website.