Nothing wrong with that, but if you are willing to forgo around 6-8%, why not make the asking price more attractive by deducting the transfer fees from it, upfront?
For example, a property that is worth 1,250,000 would be R1,164,500. To me, that's a far more marketable property and will increase interest and competition amongst potential buyers. You can also make it clear that your price is firm, no haggling.
In your suggested scenario, your only chance to seal the deal with your sweetner is once you already have a serious buyer. IMHO it won't make too much difference to a serious buyer, he has already made his mind up.