The advert implies (but makes it clear, cannot confirm) that the nine retailers named have been sidestepping the relevant taxes and duties on the Apple products they import; in doing so, they have been able to offer Apple products at far more affordable prices than what official resellers have been able to.
In response to the claims of 'grey' business practice, Core has said that it will not support or honour the warranties on any Apple products, unless these were bought through official channels, or customers could get proof from these retailers that the relevant duties and taxes were paid over the to South African Revenue Service.
Link
The comments on there are particularly good.