As a precedent, England tried a similar tactic to du Plessis during their victorious 2005 Ashes campaign. They were not charged.
Protecting and enhancing a ball to swing in myriad conditions is an art.
It's easy to differentiate if someone is hacking away at the ball with, for argument's sake, a Swiss army knife. However, dodgy practices tend to be subtle like bowlers using sandpaper in a plaster on their opposite hand, or mopping a sunscreen-soaked brow.
The task becomes further blurred when the substance might involve what the player has consumed for lunch - toffee-flavoured saliva, anyone? As one Herald newsroom wit observed, perhaps ICC-approved mints need to be introduced?
Similar debates will continue unless a law is introduced that the ball cannot be enhanced or repaired using any substance. In that scenario, boundary hoardings and other abrasive surfaces might need softening so bowlers can redress the balance in a game already tilted in the batsman's favour, particularly in abridged formats.
Fallout from the incident has been significant. A Channel Nine (the host broadcaster) reporter was roughed up by the South African team's security manager as he attempted to block du Plessis' path at Adelaide airport. Reporters had been advised they could shoot vision but not chase interviews.
Former test captain Hashim Amla fronted media surrounded by teammates on Friday, saying: "The reason everyone is here is to stand together and show solidarity to something we thought was actually a joke.
"I know Faf has done absolutely nothing wrong. I chew bubblegum while I'm fielding - do you want me to brush my teeth after lunch?
"There was no malicious intent, whatsoever."
Neither umpire in Hobart reported du Plessis, nor did Cricket Australia lodge a complaint.
However, it appears the skipper was under scrutiny. He was cautioned by the umpires during the first test at Perth regarding fielders bouncing returns to the keeper - a tactic intended to rough up one side of the ball and achieve reverse-swing.
The cross-examination returns to the field of play on Thursday in Adelaide when the final test, a day-nighter, begins.