Several bars in Darwin have been duped by fake AU$100 notes, which have bright pink text on one side.
Northern Territory police say they're investigating after at least seven incidents since Sunday.
The counterfeit notes look like the official note, except it contains bright pink text on the left side with Chinese characters, which read: "Practising coupon. Sample. For practising use only, not for circulation."
The ploy has seen a man and a woman enter a bar and buy alcohol and cigarette with the fake notes, fleeing the scene after collecting their changed.
One sharp-eyed staff member caught them out on Monday night (local time), but they escaped after being challenged.
Police believe all of the incidents are linked.
"This is a reminder for businesses to be vigilant when accepting cash transactions, in particular transactions involving $100 notes," Detective Acting Senior Sergeant Glenn Leafe said.
The fake notes are easily available online and are usually used to train foreign bank workers.