If you stand on a rooftop in Sandton — Africa’s richest square mile — you’ll see a skyline peppered with hotels. Many have been built with money that was invested thanks to a unique tax incentive, section 12J, which was launched in 2009 to entice the wealthy into financing start-up businesses.

There’s The Capital on the Park on Katherine Street, for example; opposite is the Mint Hotel; and there’s the as-yet-unopened Catalyst Hotel just a few blocks away...